pryrt is right! look at Tk::JPEG documentation:

> This is an extension for Tk which supplies JPEG format loader for Photo image type

In the Tk::Photo docs is said which image format are supported:

> At present, only GIF, XBM, XPM, BMP, JPEG, PNG and PPM/PGM formats are supported

My picwoodpecker Tk program handles all formats if you are interested. It also use XPM to produce the icon of the program itself.

> 2 - Am I using the modules correctly? Or did I forget some basic step in my code?

Think more like Photo is a container. You must instruct it to know what it holds or, only for GIFs, if it can handle automatically.

> 4 - Are there other packages/modules that offer GUI toolkits and/or image manipulation?

I'm a big fan of GD as you can see in the above linked program of mine. Among GUI toolkit you can look at Prima

L*