[stephencanon]

The difference is that the lawyers for some companies will not sign off on employees even looking at GPLv3 sources. Rightly or wrongly, this really does make a clean-room implementation impossible.

One can reasonably argue that this is stupid and not the fault of the GPL. However, it's also reality, and a real block to adoption of technologies like image formats.

[gillianseed]

Get better lawyers.

Clean-room implementation has been around for ages, I've done it professionally myself, both from source code and disassembly.

Also not every company has clueless lawyers, nor does a clean-room re-implementation of this format need to come from a company, I'd say it's more likely not.

Seriously this sounds more like GPLv3 scaremongering than anything else, I've never seen anything like this in my professional life as a developer.

edit: as for my personal preference, I think GPL is a great license for full application/solution style software, but for libraries/frameworks, I prefer permissive licensing.

[stolsvik]

+1 for the "full app/solution" vs. library/framework applicability for GPL vs. permissive: That is exactly my opinion too. When I see GPL'ed libraries, I think "try before you buy"-style open source code, and these invariably also comes with an option to buy a commercial license.