@kohlenklau has a special tallent to push me in the most positive sense! While his last idea regarding the bmp issue didn't work, it drove me on the way to the correct solution. Yeepee! 🥳   So here is the correct way to generate a CM-compatible bmp file with Gimp (it should also work with Photoshop): - your image shall be in RGB colors mode - dimensions shall be 170 x 170 pixels or below - bmp export shall be made using 24-bit encoding (this option you must chose in a box