I state that I use Multithumb. Lately I've noticed that Google does not index the images on my site.
After doing some tests I noticed that the images generated by Multithumb are automatically included in the directory / cache / multithumb_thumbs.
Native file locks the robot joomla / cache / directory, which is why the images are not detected. However, after unlocking the directory, google does not detect all uploaded images.
I asked for help to the development team, the support forum, but have not been able to solve the problem. I do not recommend the installation of this plugin.