...The png file has 4 frames: 2 for the tower, and 2 for the actual crane structure (heading east and north-east).
As an example here's my custom crane image. The image is always 256x64.
matisoncrane.png
You can create your pictures based on this one, but keep in mind the original one was created by Theo.
Of course, cranes will only appear in easy, middle and hard modes.
Thank you for sharing this! Does that crane replace one of the ingame ones, or does it add to the repertoire of cranes?
The ingame crane has the id "$crane" and contains all available cranes. If you add one with an own id it will be picked with a chance of 50%. Cranes are almost hardcoded and have therefore no features