try uploading images as binary. uploading as ascii may cause corrupt images.

ASCII Files
.htm .html .shtml .php .pl .cgi .js .cnf .css
.forward .htaccess .map .pwd .txt .grp .ctl
Binary Files
.jpg .gif .png .tif .exe .zip .sit .rar .ace
.class .mid .ra .avi .ocx .wav .mp3 .au