UMIL doesn't like a specific image and it might be size related

I've been successfully adding several instruments to UMIL, but when I tried to add the davui I got this error message:

The error message reappeared every time I tried. I changed/removed every element I could input on the Create New Instrument page and the error message kept appearing. The one thing that allowed me to successfully publish this new instrument is when I removed the image I had uploaded. But the image is in JPEG format and less than 5MB in size, so I don't know what's wrong with it! I'd love to find out, just for future reference.

This is the offending image:


Reproduce the failure by creating a new instrument in UMIL with the attached davui JPEG, then inspect the image-upload path and the displayed error. Done means identifying why this image is rejected despite being JPEG and under 5 MB, and confirming that the upload either succeeds or reports an accurate constraint.

Written by the indexing model from the issue text.