TkPNG is an open source package that adds PNG photo image support to Tcl/Tk.
Although other extensions such as Img also add support for PNG images, this
package was designed to be lightweight, not depending on libpng nor
implementing other image formats, and suitable for inclusion in the Tk core.
Tk does not currently have native support for any image formats that allow
for alpha (partial-transparency) channels, although it does have support for
alpha blending internally.