About 85% of the inline images are smaller than 8k; the average size is about 5.5k. Some have been cropped to show only part of the full size image they represent.
About 70% of the full size JPEG images are smaller than 55k; the average size is about 51k. Most are either 800x600 or 1024x768, and all were generated directly from the raw TGA output from POV-Ray.
The ABOUTGAMMA file included with xloadimage and its descendants (notably xli) by Graeme W. Gill contains more useful information about gamma correction, including the following quote:
At least two file formats do the right thing. The Utah Raster Toolkit .rle format has a semi-standard way of recording the gamma of an image. The JFIF file standard (that uses JPEG compression) specifies that the image to be encoded must have a gamma of 1.0 (ie. a linear image - but not everyone obeys the rules).
Also, Tom Fine's USENET FAQ Archive provides a sort of hypertext version of the JPEG image compression: Frequently Asked Questions document.