I have a site with several thousand images. All those images are included in the sitemap submitted to Google Webmaster Tools. The number of 'submitted' images is OK, but the number of 'indexed' is significantly lower and it is going down!I'd understand if not all of my images got indexed (however that is also not clear and very frustrating for me) but I can not understand how the indexing can go in the negative direction?!All the images stay in their place and the pages containing them remain unchanged. At least, that is the intention.
How can the number of indexed images go down in Google Webmaster Tools?
google search console;indexing;google image search
It is very rare that Google indexes 100% of any large sitemap.  I'd estimate that Google only indexes no more than 50% of the content that it crawls.   It often doesn't include content in the indexes because of:content duplicationlow quality (or lower quality than something else that it is making room for)low Pageranklow site reputationcrawl errors I have some 20,000 URL sitemaps where Google is not indexing 5 to 10 URLs at any given time.   Those are usually the ones where it got some sort of error (such as connection timeout) when Googlebot last tried to fetch them.In the case of images, there are two main things you can do to make them better indexed and ranked:Make them larger.   Google loves very large images for image search.   Google views large images as very high quality.   Any dimension less that 400px is probably hurting you quite a bit.   600px, 1000px, or even 1600px would be a much better size for image search.Use the images on higher Pagerank pages.  Images accumulate Pagerank just like pages do.  Using an image on a popular, well linked page will make the image more likely to be indexed and will make it rank better.   It doesn't matter if you <img src= the image or <a href= the image.  Either way counts for Google's ranking algorithms. Just like with pages just having a sitemap isn't sufficient to get an image indexed and ranked.   It has to be used somewhere that Googlebot can assign link juice to it.