http://www.tcl.tk/man/tcl8.4/TkCmd/photo.htm
A photo image 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 additional full color image formats.
Photo image rotation - Image scaling
DKF: Although Tk can't load images with rich alpha channels (i.e. non-trivial transparency effects like you get with some PNG images) it can display them from 8.4 onwards.
LV: Is the distinction between load and display that you make here a difference between minimally displaying the content versus displaying the content with the transparency effects?
DKF: No. Load is the process of getting the image data created in memory from a file, and display is the putting of the image on the screen (including all transparency effects, if they're present).
[Tk syntax help|Arts and crafts of Tcl-Tk programming|Category Command]