Feature or enhancement

Add support for PGM, PPM, and PNG formats to turtle.bgpic() and turtle.register_shape().

Pitch

Currently, turtle only supports GIF format for an image file,
where as the backend tkinter.PhotoImage supports PGM, PPM, and PNG formats in addition to GIF format.
If turtle supports PNG format, you can animate true color images.
(It helps teaching Python with turtle, because you can search PNG images more easily than GIF ones on Internet.)
Also it would be consistent if turtle supports all formats that tkinter supports.

Linked PRs

• gh-95371: Add support for other image formats(e.g. PNG) to the turtle… #95378