"Sounds like" or "Is" ?

I don't see how this is related to the code in the Gadgets extension either.

Going to https://commons.wikimedia.org/wiki/File:Flickr_-_europeanpeoplesparty_-_%22I_Struggle,_I_Overcome%22_-_book_launch_%2878%29.jpg?debug=true that error is triggered by jQuery which is https://commons.wikimedia.org/w/load.php?debug=true&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=vector&version=ok2tSBsQ in line 1496:

Sizzle.error = function( msg ) {
	throw new Error( "Syntax error, unrecognized expression: " + msg );
};

In T114739#1704782, @Thgoiter wrote:

"Sounds like" or "Is" ?

Your title started with "Gadget ImageAnnotator on Commons", so... :)

My browser tells me that the error is in the zoomviewer gadget, and really: https://commons.wikimedia.org/wiki/MediaWiki:Gadget-ZoomViewer.js there it is (line 11). Please ask a sysop on Commons to escape the double quotes in the page name when building the attribute selector.