Unable to Determine Size of Image

A user posted a link to this image:.

If I try to attach it to the forum I get this error message:

ERROR
It was not possible to determine the dimensions of the image. Please verify that the URL you entered is correct.

The image is a CMYK JPG image that opens fine in IrfanView.
Invalid Image.png

I suspect the library used by phpbb failed to process the image. I don’t know why.