There is just no simple way to do this currently on Ancestry's online tree.
I have two trees: ie "Smith Family Tree" and "Smith Family Tree (working copy)". I use the working copy for data that I still need to verify. The other tree is only contains facts/events/individuals with verified information.
Whenever a person makes it from my working copy to the verified tree, I create a link between the trees using Member Connect. This makes it easy to move facts from my working copy to my verified tree. I can also open both trees in separate browser windows go to the list all people screen and see who hasn't made it to the verified tree yet to determine who I still need to work on.
Using this approach also allows you to share the verified tree and keep the working copy for your own use. You can then use the earlier suggestion for changing the primary picture in your working copy to a "Done" Image for those people you have finished researching and transfered all information to your verified tree. Your verified tree would have the actual primary photo you selected for this individual.