From Portal Puzzle Wiki
The SSTV pictures are a set of pictures encoded in the dinosaur wav files. Dino 1, Dino 5, Dino 12 and Dino 17 don't have pictures because they contain Morse code and not SSTV.
Dino 2, 4, 7, 13, 16, 18, 20 & 25
These each contained four images of letter and numbers. They have a counter in the bottom left and if they are read in order results in a MD5 hash which was used to discover the BBS address.
Dino 3, 6, 10 & 19
These all contained pictures hinting at the existence of the BBS.
Dino 6 and BBS GLaDOS image combined.
Dino 9 & 11
Dino 9 have a skull and probably vacuum tubes. Dino 11 has vacuum tubes, also known as Valves in the UK, and a rooster (a cock) http://img22.imageshack.us/img22/5893/dino11.png http://www.comparestoreprices.co.uk/images/sc/schleich-colourful-rooster-crowing.jpg
Seems to be a picture of a toy cow from Fame master enterprise.
Here a side to side picture : http://img694.imageshack.us/img694/9504/cowm.jpg
Dino 22 & 23
Similar to the toy cow from Dino 15, Dino 22 & 23 relate to pictures somewhere else on the internet. In this case they relate to a flickr account containing pictures labeled "Robots and Retro". The flickr account belongs to ost, creator of the Minerva mod for HL2 and now a current employee of Valve. The flickr page has a link to his personal website.
Dino 22 is an altered picture of the "Inertial navigation system for Apollo Guidance Computer".
Dino 23 is from the same flickr photo set, but the photo is unlabelled and does not have a definition. The picture is a detail from Herbert, a robot built at MIT in 1987, implementing AI to collect and trash dropped soda cans. This could be a reference to the beginning of Half-Life 2, where a metrocop tells you to pick up a can and put it in the trash can.
Dino 7 & 20 Missing Common Border
On most of the SSTV images, you can see elements of the same black masking border design, except for in 7 and 20, as highlighted in this picture: