Engravings can be of things a dwarf likes or hates, but also of things that other dwarfs like/hate. Sometimes they engrave things they have seen recently, like flies or other vermin. I had a dwarf engrave pictures of plaster casts after he broke his arm and had to wear one for a while

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I have read somwhere that dwarfs who admire tradition are more likely to engrave historical images. There are several categories of these:
- The image of your civ and your government.
- The history of your embark region. If you embark in several biomes only one seems to count. These get engraved the most, which leads to countless images of unimportant dwarfs getting killed by something in world gen etc.
- The history of your fort. This includes the foundation of the fort, noble appointments, enemys and dwarfs getting killed, creation of artifacts and masterworks, dwarfs settling in your fort. They seem to appear in that order, so you'll have more images of the foundation of your fort than of masterful roasts.
- There seem to be almost no images of the history of your civ outside your fort/region, except on coins.
The regional thing is a bit annoying, in a fort that is 30 years old and has a lot of history I still get an awful lot of engravings of a dwarf killed by an ettin in my embark region in world gen.