In Adobe Draw, the photo is locked to the bottom - I treat it like a drawing guide or reference layer.
If you want to create additional collage pieces, you might want to think about using Draw & Sketch together.
Here's a workflow:
Once your piece is finished in Photoshop Sketch, you can send it directly to Photoshop CC. Although Sketch doesn't give you an indication of the layers, it preserves the layers that you've added as separate elements. Photoshop remembers the discreet layers and allows you to continue working on them.
Hidden feature? Maybe. But definitely worth investigating. Plus: Transfer Modes (my favorite)