Error when trying to edit metadata of JPG from shutterstock

I had the same problem.

Try opening it in a text editor, and look for the marker PNG.

It might be a png masquerading as a jpg.

I have seen this in the forums a number of times but not directly related to stock images. I have also had such problems when using some scripts.

There are usually two fixes, either using ExifTool to rebuild corrupt metadata or totally remove the offending tag or group – or sometimes it is solved simply re-saving the file as is. Something appears to get corrupted in the XMP metadata or other metadata.

Shutterstock is a stock image site. Most likely, they have locked the metadata so it can not be changed since they hold the rights to the image. Any changes to the metadata you are making is altering the data of the image which you are only using with their permission. Changing that data in any way is actually an infringement of the copyrights on the image that is owned either by Shutterstock or the original photographer. In other words, you should not be changing any of that metadata anyway.