10
sure you can, you just have to add a few lines to the imagemanager to make the script think its a png.
Or if you need gif support that bad, you can update your tcpdf. As they have finally added gif support.
Again, php != image format man.
Zhollou will need to rethink his script if he wants extgal to work with all XOOPS functions. What you need to do is stroll over to HIS website and post a bug report.
This has nothing to do with the XOOPS core. It is his module that is causing your problem.
if you look in the uploads directory the images are not stored as php