You could do that in Resolume but you'd have to create a composition that has the size you need, scale your pictures to the comp and take screenshots (under the output menu). But if you have several pics and want to have more control of the output, you're better off using software such as Adobe Lightroom or Apple Aperture to do batch changes.
If necessary, take a look at the following link to know how to do batch changes in Lightroom:
http://digital-photography-school.com/b ... lightroom/
Regardless of what you do with your images in Resolume (zoom, effects, etc...) you will get the best output if you match your composition and the size of the outputs to the native resolutions of your projectors and not have to do any mapping or keystoning. I always set my comps as an aggregate of all my projectors' resolutions and my goal is to minimize the amount of wasted pixels so I always start with a piece a paper, a pencil and a calculator but I'm old school when it comes to that.
No point in having a 2K image in a 1024x768 projector since you'll lose 75% of the information when the image is scaled down. Now if you need to zoom into a 2K image at 200%, then having a 2K image in a 1024x768 projector is perfect since you'll be showing 25% of the 2K image hence 1024x768 pixels.