To install Shotwell in OSX
As of right now there is no gexiv2 brew formula but I've created and submitted one which will hopefully get accepted soon. You can follow here: https://github.com/Homebrew/homebrew/pull/37944

Beyond that there are various dependencies of shotwell that aren't easily available through brew, for example rest and gudev which don't appear to exist anywhere for OS X. I'll have a go at creating formulas for them depending on how the first one goes.