In academic works one diagram per 500 words is a commonly recommended guideline to illustrate the text.
However, in hubs, which can and should be more visually appealing, I think between six and ten would serve a 1500 word article quite well without being too overbearing. That's just my opinion, though : ).
If it's a hub on photography then more would be fine but I agree with 1 per 500 words, otherwise it makes it hard to follow.
If it's a photography, art or craft hub, then I think photos or scans are as important as the words that describe them.
Also, how-to instructional hubs can have more photos to illustrate the instructions - I know many people who hate cookbooks that don't have photos for every couple of steps.
For stories, academic articles, etc. Then I think the number of photos can (should) be fewer, and should be topical - used to add extra information or clarity to the written information (and not only for decoration). Having said that, a 'decorative' photo, well chosen, can pull more readers to a hub.
I have never seen any information on this. There is so much about using Videos, that video stuffing is ridiculous. Maybe photo image in beginning, middle and the end.
I would favor about 6 photos but I don't think you can have a hard and fast rule. Loads of videos annoy me more.
I would say Three to Six. Anything more than six will look like a overkill.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.