Typically gamma correction should be set at 2.2 although threads here concerning this t opic recommend not using gamma correction at all.  Especially if you are using IBL with 2.2 gamma corrected HDRI images. 

Textures used from other sites should be regarded as copyrighted material unless specifically stated in writing that set material can be used for private and commercial content.  Many individuals lose sight that such property are really exclusive to the originator and they legally decide how it should be distributed and used.