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Superimpose two images to test similarity

Hi experts,
I want to place two scanned line art images on my screen and adjust their size and position so that I can visually place one on top of the other to look for similarities in shape. I know that GIF images can be made in varying degrees of transparency so that I think I should be able to do this, but I can't get any of my basic graphics programs (Paint, Corel, Serif) to do it.
Can you suggest any ways to do this and cheap (or free) software that can do the trick?
2 Solutions

First of all, GIF has only binary transparency, it's either on or off. However, other image formats do support fully variable transparency - PNG being the one most suitable for use across applications.

Having said that, any decent graphics program should be able to take your files and allow you to superimpose them to make the comparisons you want. If you want a great open-source (free) program with capabilities which approach those of Photoshop, try the GIMP, http://www.gimp.org.

In Photoshop you can adjust the transparency of any layer using the layers palette.
1. Just bring both the images in one file in two separate layers
2. reduce the opacity of the upper layer in the layers palette.

You can easily compare both the images.
You can use similar method in any other graphic software, such as Coreldraw etc.
Yup, go for the GIMP as Iherro suggested.  Very powerful and FREE!  :)
StuartOrdAuthor Commented:
Thanks for your help. I tried Gimp, and didn't find it free, but got a trial version. Looks good. However I persisted with CorelDraw as I've got some knowledge of it, but hadn't found the transparency tool before. I found that the lens tool can set the transparency of objects and would be spot on. If I import scanned bitmaps, the lens tool won't work on them. However I can use the Interactive Transparency tool on one and that works fine, especially if I put the two samples on different layers so that it's easy to fiddle with the size and position of the transparent one to get the overlay right.
So thanks for pointing me in the right direction!
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