How effective are still repeating keywords in the alt image?, If I have 100 pictures on 1 page, and all my pictures alt content with the same keywords
Hi I would suggest you to name the ALT honestly, as a user coming to your page through Google Image Search while searching for 'Jesus', will be surprised to see Celebrity Pics , just because you gave Jesus ALT name to your celeb pic - Wat will you feel then? Just anger, rt?
He raises a good point plus if for some reason your images are taking a long time to load the website may display all the alt words which for a few seconds would look ridiculous. Just keep it in mind that not everyone has fast Internet yet.
Putting to many images in your page will slow down the loading time. In 2010 google put more attention to fast loading pages. Use only relevant images in your page, the alt atribute is just one factor for onpage SEO.
I wouldn't say dupe the content, but write what a user would want to see alternate to the image loading, that is what the ALT attribute is for anyways. I always do this, and I still get traffic from both Google Images and regular Google Searches for my alt and title values