Match an image on top of another to get the correct scale

[devize]

Basically, I have been given two images, one with a key to tell distance and one without. What I have to do is match the one that is not in scale with the one that is so that I can copy the key on to the image.

Is there an easy way to go about this? What I've been trying to do is downscale the larger image, paste it on top of the image with the key, reduce the opacity and then try to match certain features. I can't get it to look quite right though. The other problem I have is that when I downscale the larger image the quality becomes very poor. Once I get the scale correct I am supposed to count the craters for a specified radius.

Here are the two images. Any help would be appreciated. Thanks!

 

[Hoogle]

not really unless you are a mathmatical genious. The images can be taken from 2 totally different focal lengths and totally different resolutions. So unless you have all the exact details of the 2 images to even begin calculating this then I really do believe your just going to have to guess.

 

[devize]

Thanks, I guess they'll have to be happy with the close enough is good enough approach then.

 

[Tom Mann]

Don't do it using Photoshop, a tool primarily for photographers, artists and designers. Use a tool designed for real image processing. What you want to do is called "image registration". One of the most common methods is through recursive cross-correlation of the two images.

I would suggest Googling {image registration matlab }. I got nearly 1 million hits that looked to be quite relevant using that search. Add terms like "code", "example", "tutorial", etc. to this search to get more detailed info. Matlab has an excellent Image Processing toolbox, and I'm sure you will have access to it through your institution.

If you aren't familiar with Matlab, you can also try Image J from NIH. Googling {image registration imagej} produced about 100,000 hits, many of which seem relevant.

HTH,

Tom M