I read some articles about HTTP headers compression. Today I installed YSlow and it recommends that I compress the resources (text/html, javascript, css and images). Now I'm reading the documentation for Apache mod_deflate but in the example don't compress images.
Should I or should I not compress images in my site?
Your images should already be compressed - any extra compression won't have any noticeable effect on filesize, but will increase processing time.
Compressing files that have already been compressed very rarely results in a reduction in filesize, and can often increase filesize.