[JohnR]

I'm so baffled by Photoshop sometimes... what I want to do is set up a set of layers that specify different crops of an image (e.g. for 4x6, 5x7, 8x10). I would prefer to not have to copy actual pixels, so I can continue to work on the base image if necessary (and also to keep file size down).

Then I want to run a batch script to generate images for all of the different crops I set up (with resizing, mode change, etc).

Can this be done? I'm looking at layer masks, vector masks, and clipping masks, and am not sure which (if any) will let me do this.

Any clues for me? 

[nathanm]

To make a series of duplicate images each with different crops:
Make an Action which duplicates the current image, crops it at a given aspect ratio and does whatever else you want and run that as a batch or make a Droplet of it. 

To see a certain crop size on your single existing image:
Make a crop tool action which HIDES instead of crops, so it would be non-destructive.

It's kind of complicated to explain, but it could be done.  Another option would be to make a Tool Preset with your desired crop size.  Additionally if you matched up the color of the crop tool's shield color (at 100%) and your Photoshop fullscreen background you would essentially have a clean view of that particular crop.

[nathanm]

Wait, maybe I misunderstood.  The layer part is confusing me.  So you want a single document, but with just a layer showing a different crop?  I guess you would use the marquee tool with an aspect ratio constraint on it and make regular layers on top of the stack filled with a solid color like white or black.  This would just visually mask off the image.  Like so: