Is there a list anywhere for items you are seeking images for?
No, but you can see which ones we know we're missing on pages like the following because we don't have a thumb nail link to a post.
Mission Rewards (Armor)
Mission Rewards (Weapons)
There are also a number of world drop armor sets and weapons we don't have, but it's a little more difficult to narrow down what those are. If they aren't on these pages, we don't have them.
World Drops (Armor)
World Drops (Weapons)
We pretty much have everything that is available from a vendor or the Cartel Market.