Google-images not indexing image tags with single quotes?

Just some plain weirdness: Google Images stopped indexing my images some time ago and I've already tried several things to improve this. Up so far I did not succeed...

I did just notice that most of the image tags of the images indexed were all done with double-quotes instead of the current single quote I'm using... Perhaps that's the answer why! So, let's see in a couple of days if the indexed images are better! :)