Vou mostrar uma solução que encontrei para facilitar minha vida na hora de definir os mime types que poderão ser aceitos pelo sistema na hora de salvar um arquivo enviado por upload. Afinal, decorar todos os mime types é difícil.

Primeiro vou criar um arquivo que conterá todos as extensões existentes e seus respectivos mime types.

O nome do arquivo é apenas MimeTypes, isso mesmo, sem extensão, apenas MimeTypes. Se estiver faltando alguma extensão, basta acrescentar na lista.

MimeTypes

The list of Mime Types(actualized in 2011-10-15)

#

The format is 2 columns:

Column #1: Extension

Column #2: MIME type

#------------------------------------------------------------------------------

.3dm x-world/x-3dmf
.3dmf x-world/x-3dmf
.a application/octet-stream
.aab application/x-authorware-bin
.aam application/x-authorware-map
.aas application/x-authorware-seg
.abc text/vnd.abc
.acgi text/html
.afl video/animaflex
.ai application/postscript
.aif audio/aiff
.aif audio/x-aiff
.aifc audio/aiff
.aifc audio/x-aiff
.aiff audio/aiff
.aiff audio/x-aiff
.aim application/x-aim
.aip text/x-audiosoft-intra
.ani application/x-navi-animation
.aos application/x-nokia-9000-communicator-add-on-software
.aps application/mime
.arc application/octet-stream
.arj application/arj
.arj application/octet-stream
.art image/x-jg
.asf video/x-ms-asf
.asm text/x-asm
.asp text/asp
.asx application/x-mplayer2
.asx video/x-ms-asf
.asx video/x-ms-asf-plugin
.au audio/basic
.au audio/x-au
.avi application/x-troff-msvideo
.avi video/avi
.avi video/msvideo
.avi video/x-msvideo
.avs video/avs-video
.bcpio application/x-bcpio
.bin application/mac-binary
.bin application/macbinary
.bin application/octet-stream
.bin application/x-binary
.bin application/x-macbinary
.bm image/bmp
.bmp image/bmp
.bmp image/x-windows-bmp
.boo application/book
.book application/book
.boz application/x-bzip2
.bsh application/x-bsh
.bz application/x-bzip
.bz2 application/x-bzip2
.c text/plain
.c text/x-c
.c++ text/plain
.cat application/vnd.ms-pki.seccat
.cc text/plain
.cc text/x-c
.ccad application/clariscad
.cco application/x-cocoa
.cdf application/cdf
.cdf application/x-cdf
.cdf application/x-netcdf
.cer application/pkix-cert
.cer application/x-x509-ca-cert
.cha application/x-chat
.chat application/x-chat
.class application/java
.class application/java-byte-code
.class application/x-java-class
.com application/octet-stream
.com text/plain
.conf text/plain
.cpio application/x-cpio
.cpp text/x-c
.cpt application/mac-compactpro
.cpt application/x-compactpro
.cpt application/x-cpt
.crl application/pkcs-crl
.crl application/pkix-crl
.crt application/pkix-cert
.crt application/x-x509-ca-cert
.crt application/x-x509-user-cert
.csh application/x-csh
.csh text/x-script.csh
.css application/x-pointplus
.css text/css
.cxx text/plain
.dcr application/x-director
.deepv application/x-deepv
.def text/plain
.der application/x-x509-ca-cert
.dif video/x-dv
.dir application/x-director
.dl video/dl
.dl video/x-dl
.doc application/msword
.dot application/msword
.dp application/commonground
.drw application/drafting
.dump application/octet-stream
.dv video/x-dv
.dvi application/x-dvi
.dwf drawing/x-dwf
.dwf model/vnd.dwf
.dwg application/acad
.dwg image/vnd.dwg
.dwg image/x-dwg
.dxf application/dxf
.dxf image/vnd.dwg
.dxf image/x-dwg
.dxr application/x-director
.el text/x-script.elisp
.elc application/x-bytecode.elisp
.elc application/x-elc
.env application/x-envoy
.eps application/postscript
.es application/x-esrehber
.etx text/x-setext
.evy application/envoy
.evy application/x-envoy
.exe application/octet-stream
.f text/plain
.f text/x-fortran
.f77 text/x-fortran
.f90 text/plain
.f90 text/x-fortran
.fdf application/vnd.fdf
.fif application/fractals
.fif image/fif
.fli video/fli
.fli video/x-fli
.flo image/florian
.flv flv-application/octet-stream
.flx text/vnd.fmi.flexstor
.fmf video/x-atomic3d-feature
.for text/plain
.for text/x-fortran
.fpx image/vnd.fpx
.fpx image/vnd.net-fpx
.frl application/freeloader
.funk audio/make
.g text/plain
.g3 image/g3fax
.gif image/gif
.gl video/gl
.gl video/x-gl
.gsd audio/x-gsm
.gsm audio/x-gsm
.gsp application/x-gsp
.gss application/x-gss
.gtar application/x-gtar
.gz application/x-compressed
.gz application/x-gzip
.gzip application/x-gzip
.gzip multipart/x-gzip
.h text/plain
.h text/x-h
.hdf application/x-hdf
.help application/x-helpfile
.hgl application/vnd.hp-hpgl
.hh text/plain
.hh text/x-h
.hlb text/x-script
.hlp application/hlp
.hlp application/x-helpfile
.hlp application/x-winhelp
.hpg application/vnd.hp-hpgl
.hpgl application/vnd.hp-hpgl
.hqx application/binhex
.hqx application/binhex4
.hqx application/mac-binhex
.hqx application/mac-binhex40
.hqx application/x-binhex40
.hqx application/x-mac-binhex40
.hta application/hta
.htc text/x-component
.htm text/html
.html text/html
.htmls text/html
.htt text/webviewhtml
.htx text/html
.ice x-conference/x-cooltalk
.ico image/x-icon
.idc text/plain
.ief image/ief
.iefs image/ief
.iges application/iges
.iges model/iges
.igs application/iges
.igs model/iges
.ima application/x-ima
.imap application/x-httpd-imap
.inf application/inf
.ins application/x-internett-signup
.ip application/x-ip2
.isu video/x-isvideo
.it audio/it
.iv application/x-inventor
.ivr i-world/i-vrml
.ivy application/x-livescreen
.jam audio/x-jam
.jav text/plain
.jav text/x-java-source
.java text/plain
.java text/x-java-source
.jcm application/x-java-commerce
.jfif image/jpeg
.jfif image/pjpeg
.jfif-tbnl image/jpeg
.jpe image/jpeg
.jpe image/pjpeg
.jpeg image/jpeg
.jpeg image/pjpeg
.jpg image/jpeg
.jpg image/pjpeg
.jps image/x-jps
.js application/x-javascript
.jut image/jutvision
.kar audio/midi
.kar music/x-karaoke
.ksh application/x-ksh
.ksh text/x-script.ksh
.la audio/nspaudio
.la audio/x-nspaudio
.lam audio/x-liveaudio
.latex application/x-latex
.lha application/lha
.lha application/octet-stream
.lha application/x-lha
.lhx application/octet-stream
.list text/plain
.lma audio/nspaudio
.lma audio/x-nspaudio
.log text/plain
.lsp application/x-lisp
.lsp text/x-script.lisp
.lst text/plain
.lsx text/x-la-asf
.ltx application/x-latex
.lzh application/octet-stream
.lzh application/x-lzh
.lzx application/lzx
.lzx application/octet-stream
.lzx application/x-lzx
.m text/plain
.m text/x-m
.m1v video/mpeg
.m2a audio/mpeg
.m2v video/mpeg
.m3u audio/x-mpequrl
.man application/x-troff-man
.map application/x-navimap
.mar text/plain
.mbd application/mbedlet
.mc$ application/x-magic-cap-package-1.0
.mcd application/mcad
.mcd application/x-mathcad
.mcf image/vasa
.mcf text/mcf
.mcp application/netmc
.me application/x-troff-me
.mht message/rfc822
.mhtml message/rfc822
.mid application/x-midi
.mid audio/midi
.mid audio/x-mid
.mid audio/x-midi
.mid music/crescendo
.mid x-music/x-midi
.midi application/x-midi
.midi audio/midi
.midi audio/x-mid
.midi audio/x-midi
.midi music/crescendo
.midi x-music/x-midi
.mif application/x-frame
.mif application/x-mif
.mime message/rfc822
.mime www/mime
.mjf audio/x-vnd.audioexplosion.mjuicemediafile
.mjpg video/x-motion-jpeg
.mm application/base64
.mm application/x-meme
.mme application/base64
.mod audio/mod
.mod audio/x-mod
.moov video/quicktime
.mov video/quicktime
.movie video/x-sgi-movie
.mp2 audio/mpeg
.mp2 audio/x-mpeg
.mp2 video/mpeg
.mp2 video/x-mpeg
.mp2 video/x-mpeq2a
.mp3 audio/mpeg3
.mp3 audio/x-mpeg-3
.mp3 video/mpeg
.mp3 video/x-mpeg
.mpa audio/mpeg
.mpa video/mpeg
.mpc application/x-project
.mpe video/mpeg
.mpeg video/mpeg
.mpg audio/mpeg
.mpg video/mpeg
.mpga audio/mpeg
.mpp application/vnd.ms-project
.mpt application/x-project
.mpv application/x-project
.mpx application/x-project
.mrc application/marc
.ms application/x-troff-ms
.mv video/x-sgi-movie
.my audio/make
.mzz application/x-vnd.audioexplosion.mzz
.nap image/naplps
.naplps image/naplps
.nc application/x-netcdf
.ncm application/vnd.nokia.configuration-message
.nif image/x-niff
.niff image/x-niff
.nix application/x-mix-transfer
.nsc application/x-conference
.nvd application/x-navidoc
.o application/octet-stream
.oda application/oda
.omc application/x-omc
.omcd application/x-omcdatamaker
.omcr application/x-omcregerator
.p text/x-pascal
.p10 application/pkcs10
.p10 application/x-pkcs10
.p12 application/pkcs-12
.p12 application/x-pkcs12
.p7a application/x-pkcs7-signature
.p7c application/pkcs7-mime
.p7c application/x-pkcs7-mime
.p7m application/pkcs7-mime
.p7m application/x-pkcs7-mime
.p7r application/x-pkcs7-certreqresp
.p7s application/pkcs7-signature
.part application/pro_eng
.pas text/pascal
.pbm image/x-portable-bitmap
.pcl application/vnd.hp-pcl
.pcl application/x-pcl
.pct image/x-pict
.pcx image/x-pcx
.pdb chemical/x-pdb
.pdf application/pdf
.pfunk audio/make
.pfunk audio/make.my.funk
.pgm image/x-portable-graymap
.pgm image/x-portable-greymap
.pic image/pict
.pict image/pict
.pkg application/x-newton-compatible-pkg
.pko application/vnd.ms-pki.pko
.pl text/plain
.pl text/x-script.perl
.plx application/x-pixclscript
.pm image/x-xpixmap
.pm text/x-script.perl-module
.pm4 application/x-pagemaker
.pm5 application/x-pagemaker
.png image/png
.pnm application/x-portable-anymap
.pnm image/x-portable-anymap
.pot application/mspowerpoint
.pot application/vnd.ms-powerpoint
.pov model/x-pov
.ppa application/vnd.ms-powerpoint
.ppm image/x-portable-pixmap
.pps application/mspowerpoint
.pps application/vnd.ms-powerpoint
.ppt application/mspowerpoint
.ppt application/powerpoint
.ppt application/vnd.ms-powerpoint
.ppt application/x-mspowerpoint
.ppz application/mspowerpoint
.pre application/x-freelance
.prt application/pro_eng
.ps application/postscript
.psd application/octet-stream
.pvu paleovu/x-pv
.pwz application/vnd.ms-powerpoint
.py text/x-script.phyton
.pyc applicaiton/x-bytecode.python
.qcp audio/vnd.qcelp
.qd3 x-world/x-3dmf
.qd3d x-world/x-3dmf
.qif image/x-quicktime
.qt video/quicktime
.qtc video/x-qtc
.qti image/x-quicktime
.qtif image/x-quicktime
.ra audio/x-pn-realaudio
.ra audio/x-pn-realaudio-plugin
.ra audio/x-realaudio
.ram audio/x-pn-realaudio
.ras application/x-cmu-raster
.ras image/cmu-raster
.ras image/x-cmu-raster
.rast image/cmu-raster
.rexx text/x-script.rexx
.rf image/vnd.rn-realflash
.rgb image/x-rgb
.rm application/vnd.rn-realmedia
.rm audio/x-pn-realaudio
.rmi audio/mid
.rmm audio/x-pn-realaudio
.rmp audio/x-pn-realaudio
.rmp audio/x-pn-realaudio-plugin
.rng application/ringing-tones
.rng application/vnd.nokia.ringing-tone
.rnx application/vnd.rn-realplayer
.roff application/x-troff
.rp image/vnd.rn-realpix
.rpm audio/x-pn-realaudio-plugin
.rt text/richtext
.rt text/vnd.rn-realtext
.rtf application/rtf
.rtf application/x-rtf
.rtf text/richtext
.rtx application/rtf
.rtx text/richtext
.rv video/vnd.rn-realvideo
.s text/x-asm
.s3m audio/s3m
.saveme application/octet-stream
.sbk application/x-tbook
.scm application/x-lotusscreencam
.scm text/x-script.guile
.scm text/x-script.scheme
.scm video/x-scm
.sdml text/plain
.sdp application/sdp
.sdp application/x-sdp
.sdr application/sounder
.sea application/sea
.sea application/x-sea
.set application/set
.sgm text/sgml
.sgm text/x-sgml
.sgml text/sgml
.sgml text/x-sgml
.sh application/x-bsh
.sh application/x-sh
.sh application/x-shar
.sh text/x-script.sh
.shar application/x-bsh
.shar application/x-shar
.shtml text/html
.shtml text/x-server-parsed-html
.sid audio/x-psid
.sit application/x-sit
.sit application/x-stuffit
.skd application/x-koan
.skm application/x-koan
.skp application/x-koan
.skt application/x-koan
.sl application/x-seelogo
.smi application/smil
.smil application/smil
.snd audio/basic
.snd audio/x-adpcm
.sol application/solids
.spc application/x-pkcs7-certificates
.spc text/x-speech
.spl application/futuresplash
.spr application/x-sprite
.sprite application/x-sprite
.src application/x-wais-source
.ssi text/x-server-parsed-html
.ssm application/streamingmedia
.sst application/vnd.ms-pki.certstore
.step application/step
.stl application/sla
.stl application/vnd.ms-pki.stl
.stl application/x-navistyle
.stp application/step
.sv4cpio application/x-sv4cpio
.sv4crc application/x-sv4crc
.svf image/vnd.dwg
.svf image/x-dwg
.svr application/x-world
.svr x-world/x-svr
.swf application/x-shockwave-flash
.t application/x-troff
.talk text/x-speech
.tar application/x-tar
.tbk application/toolbook
.tbk application/x-tbook
.tcl application/x-tcl
.tcl text/x-script.tcl
.tcsh text/x-script.tcsh
.tex application/x-tex
.texi application/x-texinfo
.texinfo application/x-texinfo
.text application/plain
.text text/plain
.tgz application/gnutar
.tgz application/x-compressed
.tif image/tiff
.tif image/x-tiff
.tiff image/tiff
.tiff image/x-tiff
.tr application/x-troff
.tsi audio/tsp-audio
.tsp application/dsptype
.tsp audio/tsplayer
.tsv text/tab-separated-values
.turbot image/florian
.txt text/plain
.uil text/x-uil
.uni text/uri-list
.unis text/uri-list
.unv application/i-deas
.uri text/uri-list
.uris text/uri-list
.ustar application/x-ustar
.ustar multipart/x-ustar
.uu application/octet-stream
.uu text/x-uuencode
.uue text/x-uuencode
.vcd application/x-cdlink
.vcs text/x-vcalendar
.vda application/vda
.vdo video/vdo
.vew application/groupwise
.viv video/vivo
.viv video/vnd.vivo
.vivo video/vivo
.vivo video/vnd.vivo
.vmd application/vocaltec-media-desc
.vmf application/vocaltec-media-file
.voc audio/voc
.voc audio/x-voc
.vos video/vosaic
.vox audio/voxware
.vqe audio/x-twinvq-plugin
.vqf audio/x-twinvq
.vql audio/x-twinvq-plugin
.vrml application/x-vrml
.vrml model/vrml
.vrml x-world/x-vrml
.vrt x-world/x-vrt
.vsd application/x-visio
.vst application/x-visio
.vsw application/x-visio
.w60 application/wordperfect6.0
.w61 application/wordperfect6.1
.w6w application/msword
.wav audio/wav
.wav audio/x-wav
.wb1 application/x-qpro
.wbmp image/vnd.wap.wbmp
.web application/vnd.xara
.wiz application/msword
.wk1 application/x-123
.wmf windows/metafile
.wml text/vnd.wap.wml
.wmlc application/vnd.wap.wmlc
.wmls text/vnd.wap.wmlscript
.wmlsc application/vnd.wap.wmlscriptc
.word application/msword
.wp application/wordperfect
.wp5 application/wordperfect
.wp5 application/wordperfect6.0
.wp6 application/wordperfect
.wpd application/wordperfect
.wpd application/x-wpwin
.wq1 application/x-lotus
.wri application/mswrite
.wri application/x-wri
.wrl application/x-world
.wrl model/vrml
.wrl x-world/x-vrml
.wrz model/vrml
.wrz x-world/x-vrml
.wsc text/scriplet
.wsrc application/x-wais-source
.wtk application/x-wintalk
.xbm image/x-xbitmap
.xbm image/x-xbm
.xbm image/xbm
.xdr video/x-amt-demorun
.xgz xgl/drawing
.xif image/vnd.xiff
.xl application/excel
.xla application/excel
.xla application/x-excel
.xla application/x-msexcel
.xlb application/excel
.xlb application/vnd.ms-excel
.xlb application/x-excel
.xlc application/excel
.xlc application/vnd.ms-excel
.xlc application/x-excel
.xld application/excel
.xld application/x-excel
.xlk application/excel
.xlk application/x-excel
.xll application/excel
.xll application/vnd.ms-excel
.xll application/x-excel
.xlm application/excel
.xlm application/vnd.ms-excel
.xlm application/x-excel
.xls application/excel
.xls application/vnd.ms-excel
.xls application/x-excel
.xls application/x-msexcel
.xlt application/excel
.xlt application/x-excel
.xlv application/excel
.xlv application/x-excel
.xlw application/excel
.xlw application/vnd.ms-excel
.xlw application/x-excel
.xlw application/x-msexcel
.xm audio/xm
.xml application/xml
.xml text/xml
.xmz xgl/movie
.xpix application/x-vnd.ls-xpix
.xpm image/x-xpixmap
.xpm image/xpm
.x-png image/png
.xsr video/x-amt-showrun
.xwd image/x-xwd
.xwd image/x-xwindowdump
.xyz chemical/x-pdb
.z application/x-compress
.z application/x-compressed
.zip application/x-compressed
.zip application/x-zip-compressed
.zip application/zip
.zip multipart/x-zip
.zoo application/octet-stream
.zsh text/x-script.zsh

Agora o script que irá buscar os mime types corretos para cada extensão informada.

<?php
/**
* Define um array de mime types permitidos com base na extensão
* @param array $extensions O array com as extensões permitidas
* @return array Os mime types possíveis das extensões
*/
function getMimeTypes( array $extensions )
{

 $mimes = file_get_contents( 'MimeTypes', FILE_USE_INCLUDE_PATH );
 $mime_types = array( );
 foreach( $extensions as $search )
 {
 preg_match_all( sprintf( '/^.%s[^\n\r]+/mi', $search ), $mimes, $matches );
 $mime_types = array_merge( $mime_types, preg_replace( '/^[\S]+[[:space:]]+/', null, $matches[ 0 ] ) );
 }
 return $mime_types;
}

Teste

<?php

var_dump( getMimeTypes( array( 'jpg', 'gif', 'png', 'zip' ) ) );

/**

array

 0 => string 'image/jpeg' (length=10)
 1 => string 'image/pjpeg' (length=11)
 2 => string 'image/gif' (length=9)
 3 => string 'image/png' (length=9)
 4 => string 'application/x-compressed' (length=24)
 5 => string 'application/x-zip-compressed' (length=28)
 6 => string 'application/zip' (length=15)
 7 => string 'multipart/x-zip' (length=15)

*/

Como usar

<?php

// Pega o mime type do arquivo enviado

$finfo = new finfo( FILEINFO_MIME_TYPE );
$mime_type_arquivo = $finfo->file( $_FILES[ 'userfile' ] [ 'tmp_name' ] ); // O nome temporário do arquivo, como foi guardado no servidor

// Pega os mime types associados a cada extensão permitida
$mime_types_permitidos = getMimeTypes( array( 'jpg', 'gif' ) );

if( in_array( $mime_type_arquivo, $mime_types_permitidos ) )
{

 echo 'Arquivo válido!';
}

else
{

 echo 'Arquivo negado!';
}

É isso pessoal. :thumbsup: