Originally Posted by Blaqk Majik
Yeah they are dropped randomly throughout the new CoC DLC. It's been rumored that BadAsses drop them but I have had them drop from normal enemies. A lot of people have just been farming Pyro Pete's Bar Room Brawl Tier 3 Rematch to get them. 10 are required for the achievement but it's also been known to not unlock til after you get at least 12-15 for some reason.
it can take far more if your not lucky, this is due to the fact that there are actually 3 different versions of moxxi pictures and only one of the three counts towards the achievement progress. it is not a glitch, and also i would recommend pyro pete's bar, on TVHM, with your vault hunters relic equipped to slightly increase your chances of getting the right one.