I couldn't find a part number on the inverter board, any ideas on how to get a replacement?
What Jerry said.
But there are a number of sites on the internet that specialise in replacement CCFL and inverters.
Typically both are very cheap, but a real pain to replace (CCFL especially). I'll try to drag up one of these sites.
Are you in the US? If not, postage may kill you. I flew over there from Australia to pick mine up (just kidding -- I had it sent to me while I was in the US though).
OK, you could try
http://www.lcdparts.net/ I'm pretty sure I didn't purchase mine from them, but the site seems to have all the same relevant information. You might try looking for replacement parts for the model of photo frame you have. The CCFL typically runs along one of the long edges of the display, so that should tell you the size you need.