STM32H747 Hardware JPEG Compatibility issue

Dear all, I have successfully implemented the example STM32CubeH7-master\Projects\STM32H747I-DISCO\Examples\JPEG\JPEG_DecodingFromFLASH_DMA with the image file given as C source there.

Now I wanted to change the image data, which however was not successful, so I tried the following:

• took the image_320_240_jpg.h file and on PC wrote it to disk (example.jpg) , then converted it to a c file again and used that: Success, no change
• opened example.jpg, saved it with Gimp as example2.jpg with quality 75 to decrease file size: Fails during HAL_JPEG_Decode
• opened example.jpg in MS Windows 10 Paint and saved it as example3.jpg (no parameters available, file beacme bigger): Success
• created some weird image in MS Paint (example4.jpg:( Success
• opened and saved in Gimp again (example5.jpg:( Fail during HAL_JPEG_Decode

Am I missing any jpeg features I need to avoid? Are there any other programs known to be working outside of MS Paint, preferably some where you can adjust the image quality vs. file size?

These are the images:

example.jpg (Original from example, working):example2.jpg (fails):

example3.jpg (working):

example4.jpg (working):

example5.jpg (fails):