It would be nice if you'd show evedence that things look fine on your end.  Copy the same image I did from the following page...

http://excalibur.renderosity.com/mod/gallery/index.php?image_id=1235392

Look at the jaggies my my signature, as well as on the petals of the lilly.

Terranuts.com does the very same thing.  The image resizing by whatever gallery software he's using also does a poor job at resizing.  As a matter of fact, I've yet to find a PHP gallery that does a good job at it.