The only program intended to view .Snag files, is SnagIt.
We do NOT expect customers to share .snag/.snagproj files directly. We do not hold forth .snag/.snagproj files as formats for universal interchange. In fact, Snagit's primary workflows are specifically designed to make it VERY easy for customers to share in universally accepted formats (.jpg/.png, etc) - and that is how we intend for it to be used.
- Doug Troxell, Employee @ TechSmith
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You misunderstand the SNAG file, it's used to maintain any modifications the user made viable rather than having them flattened as would happen in a normal image format. It's primary purpose is for the user to go back and change any modifications they made. There's nothing evil in this purpose at all. It's not for sharing but for the user to modify their captures.
- Manny Carvalho, Champion
Source of quotes: How does a non-SnagIt user view .snag files?