Many　image　data　are　usually　archived　and　transmitted　in　the　compressed　form[1],　for　example,　JPEG.　Traditionally,　manipulating　the　JPEG　image　must　fully　decompress　first.　Because　the　traditional　method　is　not　efficient,　it　can　not　satisfy　the　requirements　of　real-time　system.　so,　studying　the　technology　of　image　processing　based　on　DCT　compressed　domain　is　urgent.　This　paper　describes　the　JPEG　compressed　algorithm,　the　method　of　DCT　compressed　domain　image　processing　and　the　location　of　the　image　processing　in　DCT　compressed　domain.　©　2011　IEEE.