> +www.example.com/*exemple*.png*[<100]
> -mime:*/* +mime:text/html +mime:image/*

I don't think you can filter by mime type.  
You need a space between the < and the 100
Normally httrack will stay on the same site, so just +*example*.png will
work.
 
> Also, I would like to know how to download only
> pictures.

You need the html's also unless you know all the image urls