How to mask an imported image as a plane? I just want to make a mask for an image as plane like in Gimp or any Image Editor.

I have a transparent drawing and I want to "fill" some parts of that drawing with other images as planes and other parts fills with materials.

I have a video that shows an example of what I want to do (of somebody doing it in After Effects): https://youtu.be/wSeOrwoe5r8

Thanks.
What you can try to do, is using the image that you want to be filled with the transparent image, and convert it with a Color Ramp. This will work if you have a lot of contrast in that image. Here the Node setup: