I bought a cardboard Luckies SmartPhone Projector on Amazon for £8.00 and it works well enough, in a dark place!
Here’s a picture I’m planning to paint, (taken with an iPhone Camera in “panorama” mode) and the trace I made over the projection:
You might notice the image was “reversed” by the projector!
I tried again, after reversing the image in the phone, using Google Snapseed first:
And here’s the watercolour: