I have a web site with a lot of web-pages and images. I created the sitemaps (grouped into single sitemaps index file). I submitted those sitemaps to Google but the indexing process is disappointingly slow:

Sitemaps was submitted on Feb. 4th. Submitting process started on Feb. 8th and so on:
02/09/2014 - Indexed 187 images
02/10/2014 - 956
02/11/2014 - 1180
02/12/2014 - 1196
02/13/2014 - 1198
02/14/2014 - 1192 (!!!)
02/15/2014 - 561 (!!!)
02/16/2014 - 1144
02/17/2014 - 1144
So the images indexing process is weird.
However the crawling process look much more attractive and promising:

Do I need to wait some extra time? Or do I need to take some actions to help Google to index my web-site correctly?