ESP released an updated IDE (1.0.5, then 1.0.6), and while I had checked it did not break my build I had not realised that they added some extra resolutions to the camera, which in turn messed with the 'resolution' setting.
I've now fixed this on the master branch in GitHub, and I'll bang a V3.1 release out asap with the fix.
As a nice consequence the sketch has gained some extra modes, including a 96x96 thumbnail, HD-720p and (on 3MP camera equipped modules) FHD-1080p.
NOTE: there is a ESP IDE V2 beta out, I have not tried compiling with this but I believe it will fail. I'll sort that out once it is out of beta, ESP are a bit erratic about this.