Yeah, the whole "Image Brush" feature is still only a preview of what's to come! I apologize for that, but had to share it already!
You see the small GUI piece in the upper left corner?! It has a number of buttons to control how the image/images are being used. You can make as many images as you like and then play them back during painting either in sequence, at random or based on your pressure as well as the default "=" mode, which only paints with one image of your choosing. I still have to make a video about all these features, because it's a little bit more complex.
Brush #9 and #10 work with images, while brush#9 has the option to use images or not. By default it does not use images. You can also decide, if you want to use the whole image, including material, or only color or only material, but that, too, is a bit complex. I need to make a tutorial, but more than that I need to make a PROPER GUI for all this.
Anyway, lots to explore for you and lots to do for me!