http://www.tcl.tk/man/tcl8.4/TkCmd/photo.htm
A photo widget is the means that Tk uses to display full color images. Tk comes with support for GIF, PPM, and PGM formats, as well as a format to hook in code for other formats. The Img extension provides some additional full color image formats.
See also image
Photo image rotation - Image scaling
Tk syntax help - Arts and crafts of Tcl-Tk programming - Category Command