layers

[oartisto]

Can you take a photo and turn it into a transparency that has all of the details but is no longer opaque then it can be laid over another photo? 

[David Asch]

It depends what you mean by transparency. You can import a layer into another image and lower its overall opacity; the opaque areas will become more translucent as you reduce it. You can also use layer blend modes to change the way the layers interact with eachother.

You can also make a selection of the part of the image you want to remain completely opaque and turn it into a new layer. The rest of the layer will be transparent.