It requires imageapi_gd or imageapi_imagemagick or any ImageAPI toolkit to work.
ImageAPI Optimize allows you to use your preferred toolkit and optimize (losslessly) the image when it is saved.
This module needs optional external commands.
The size reduction varies on the original image, normally between 10-30 KB if image is not optimized before.
Unfortunately all metadata is removed, but optimizations are lossless.
Unpack in your modules folder (usually '/sites/all/modules/')
Enable under Administer > Site Building > Modules
Here are some key features of "ImageAPI Optimize":
· Optimize JPEG images. Requires jpegtran (probably available in your system), jfifremove (you compile it yourself)
· Optimize PNG images. Requires OptiPNG, AdvPNG (since 1.2).
· Other formats/utilities are to be added.
· Drupal 6.x