What license is most similar to GPL 2.0 but for stuff other than code like images and documentation?
The GPL can be used for any copyrightable work, including images and text. People who distribute such work under the GPL will need to supply the "corresponding source" for making modifications which may simply be the work itself, or some more malleable format (e.g., an image may have been made from a file with editable layers in Photoshop or GIMP, or a PDF document may have been created from LaTeX source).
Alternatively, Creative Commons Attribution-ShareAlike (CC BY-SA) is a weaker copyleft license intended for artistic works. It is notably weaker than the GPL because it does not require the distribution of corresponding source. If someone distributes a modified work based on a CC BY-SA work, then that new work must also be licensed under CC BY-SA, but the distributor does not need to supply their underlying source. This means recipients may legally distribute and modify that work further, but in practice it may be very difficult to make modifications without corresponding source.
The FSF recommends the GNU Free Documentation license (GFDL) for software documentation. However, this license is GPL-incompatible and (in this writer's opinion) rather complex and cumbersome. Wikipedia has a good overview of its complexities.