You do not have a license.

[lambdacat]

I'm not a lawyer, nothing here is legal advice blah blah blah, just pointing this out.

I would like to use this wrapper in a proprietary project. Is it licensed similarly to libpng itself?

If you're not aware (which I hope you are, considering that you've written this wrapper) libpng is released under its own license, which you can read at http://www.libpng.org/pub/png/src/libpng-LICENSE.txt

It would be rather convenient if you could release your wrapper under something BSD-ish or similar =].

[metajack]

I believe our intention is to license it the same as Rust, which is MIT and APLv2 I think. I'll try and get this updated ASAP.

[jpernst]

I've been wondering the same thing. Most of this wrapper appears to be Apache/MIT dual, with the exception of shim.c, which is MPL2. That should probably be replaced to make the situation more uniform.