I don't know if this has been posted before, but I stumbled across this presentation which is an extremely thorough overview of the photography of fish specimens. - "Photography basics and setting up a 2D imaging station", John P. Sullivan, iDigBio Vertebrate Digitization Workshop, Berkeley, CA, April 4-6, 2016.
PDF of the Powerpoint available here and the recording here (requires Adobe Connect, starts @ 0:32:16 and ends at 1:15:00)
The following presentation looks useful as well - "2D Image Processing Software", Andrew Williston
I have been searching for something similar for some time now as I'm trying to figure out the ins and outs of specimen photography.
I'm excited about finding it and I figured others here would appreciate it as well.