I was wondering if someone knows how many days or months does it take for Google to remove the dead sites from their index? I've made test websites with tags for hosting images and texts, let it stay for a month and then deleted them quite after. I tried searching them and they still appear there. Any idea how many days does it take before they completely remove the dead sites?
How long will it take for Google to unindex dead websites?
google index
Deleting or blocking the images is a necessary step, but only the first step to get your images de-indexed. Especially if you want the images to be removed quickly. I would recommend you sign up for a google webmasters account and then report that the images no longer exist and that they should be taken off the index. Google has put up a form where you can report images and URLs  but it can be a bit hard to find: Webmasters > Tools > Removal.In my experience the images should disappear within 2448 hours. Some time ago I have written a short beginners guide about the process with some more details over here.