Well, On Google Images research page you find plenty of images published on Waterwind.it, but they are the ones which I inserted into the articles. That's the case you quoted. But, I never get an Eventgallery page related to any Event I created, on Google.
I have Google Search Console, and I discovered that, if I check any Eventgallery page with slidegallery of my site, they are not indexed at all.
This clue was useful to understand the reason of the problem....
I use Jsitemap Pro to create the sitemaps I send to Google.
Jsitemap is able to create almost automatically Data Sources for the sitemaps picking info up from many extensions, like Kunena, K2, etc.. Unfortunately, Eventgallery is not included.
So, I had to configure Jisitemap Pro in order to pick data also up from Eventgallery.
It was a big labour, but probably worth of being done.
You can check the result here: https://www.waterwind.it/new/index.php?option=com_jmap&view=sitemap&lang=en&dataset=3
Now, I think that the problem will shortly be solved. Just the time for Google to index all the new Eventgallery pages. Checking on my Google Search Console, it seems that Eventgallery pages are going to be indexed.
Regards