As first, to become sure, whether Google makes indeed notice about your images, make use of "fetch as Google" function in your Search Console.
If on fetching as Google
alt are in the place, do the next check: make a
site query into Google web search, open
cache-version of your page and look into the source code - are
altthere in the place?
If both tests are positive - than just wait, make an image sitemap, share it into Search Console, than wait again - you had make doubly sure, that technically everything is ok.