Manual:$wgIgnoreImageErrors/en

Details
If true, inline scaled images will still produce $img tags ready for output instead of showing an error message.

This may be useful if errors are transitory, especially if the site is configured to automatically render thumbnails on request.

On the other hand, it may obscure error conditions from debugging. Enable the debug log or the 'thumbnail' log group to make sure errors are logged to a file for review.