Thank for this quick answer
It works

For other people, if it can help

I have tried first
parameter for 'images/videos sitemap = 50' to 10 links for each step
It was not enough, precaching always not working

Then I was in data source and for each of them I have specified if I wanted it in the sitemap image
For exemple I have included the virtuemart products but not the categories
and not all the article for example I have no interessant image in my legal directory.

And last I don't know if it is important
I had not the same value in data source and in general configuration for the images I wanted to exclude (email, template...). I have copy the same list in data source and in general configuration

Now precaching is working for approximatly 3500 images

Thanks a lot