The logos of the Debian derivatives registered in the derivatives census are overwhelmingly stored in PNG format, with a handful of JPEG and GIF images. One derivative (LMDE) doesn't have a logo registered in the census.
Half of the logo image files have some embedded indication of which program was used to create them or which program they passed through last.
Just over half of these were created with some proprietary Adobe or Macromedia program. The one that surprised me was Emdebian's logo indicating it was created in Adobe Photoshop 3.0, but to be fair it looks like several of the Debian logo files were also created in Adobe Photoshop 3.0 so that might just be copied from the Debian logos. Two of the logos have an easter-egg reminding everyone who looks about the obsession some part of Adobe has with rubber ducks.
Just under half of them were created using Free Software, with most of those being produced in the GIMP and a few in Inkscape.
One of them looks like a derivative work of the KDE logo. Two of them incorporate the Debian swirl indicating their Debian heritage. Two of them in some way incorporate the Tux Linux mascot indicating that they use Linux. One of the logos contains the word Debian and one contains "sid". Three of the logos mention both GNU and Linux and another mentions only GNU. One of them mentions the government organisation sponsoring the distro (LinEx).
A few logos consist solely of text and a few have no text, but most combine both elements. Three have some indication of a URL in them. Several of them have some sort of indication of what the distribution's focus is.
One has Adobe's XMP XML cruft embedded in it indicating document identifiers and two logos have an embedded ICC profile. One logo has the author's name in it.