I wanted to share that the very nice real effort tasks that can be found here: https://www.otreehub.com/projects/otree-realeffort/
need pillow <10 (e.g. pillow 9.5.0) to run on a linux server - at least using the decoding task. The newer pillow 10 does not show the picture.

The error was something like:
 ... in render_image
    w, h = draw.textsize(coded_word)
           ^^^^^^^^^^^^^
AttributeError: 'ImageDraw' object has no attribute 'textsize'

Thanks! I will fix them. Actually I’m gonna release a big update to them soon, good to know this issue.