I opened this with a sense of puzzlement: just what is a doom painting anyway?
All was soon revealed. A doom painting is a mediaeval depiction of the Last Judgement, as taught by Christianity, that was a popular adornment of churches in England... and the reason why so many old English churches have white-washed walls these days, a relic of Puritain distain of such art in the 17th century! Whilst a lot of the iconography of a traditional doom painting would be inappropriate in most fantasy worlds - as they don't tend to practise Christianity there - the base concept is ripe with possibilities, from depicting the tenets of whatever deities are revered there to enabling the GM to weave subtle forshadowings of his plots into artwork which the characters may or may not notice. You could even provide hints about an impending trap... or the painting itself could be a part of that trap!
The first table provides suggestions for the overall appearance of the painting. One interesting feature is the two-sided nature of each work: this is completely traditional and harks back to the Last Judgement theme of real-world doom paintings. One side would depict what happened to good folks (welcomed into heaven) and the other side showed the evil people being consigned to the fiery pits of hell! So here you might see something like "A king and queen are seated in this painting. All those who have approached the king have been decapitated, while those who have approached the queen are showered with fine gifts." (#84-86). You can be as cryptic or as blatent as you like: the images are best presented without commentary to let the characters make of them what they will.
The next table is entitled Dressings and Features, and offers various additional features that might add interest. Perhaps the doom painting is upside down, or has been defaced or partly covered over... or maybe it has an ornate frame. You will have to decide if the feature has any significance, or if it's just something done by a previous party of adventurers...
Finally comes a selection of traps and tricks that can be incorporated into your doom paintings. Now, there were some in the first table, but here five new paintings are described in detail along with the awful things that might befall anyone who stops to take a look.
Now, I'd suggest that you use doom paintings sparingly - unless there's a very good reason, like whoever constructed the dungeon being an art collector - but a well considered one could provide a potent and memorable dungeon feature. If you visit one of my dungeons in the future, watch the walls...
[5 of 5 Stars!]