Spawn Foliage from greyscale image

Deceptive question I know… But here we go.

Is there any way to procedurally spawn foliage/trees etc from an image. Grayscale or otherwise! I have an area of terrain which is identified as trees in a png image, I want to use the image to spawn trees to quickly create the landscape needed.

I haven’t been able to find info… so this is either crazy easy and everyone knows already, or crazy hard… but maybe there is a link to info/tutorial I have missed?

Thanks for info guys… any more from me to make this clearer - no problem!!