The pthreads based multi-threading code should be improved (IMHO). I see two options:

1. keep the internal 'explicit' interface more or less like it is but switch from pthreads to c++11 threads.
2. remove the 'explicit' interface, which should simplify the code significantly and switch to OpenMP where applicable.

I would strongly prefer the second option as is would reduce the complexity of

At the first image of the icon view, when you mouse-over the thumb to get the info tooltip, it is trying to draw it half outside the screen and it only flickers without showing properly.

Workaround: If you hover on the next image and get the tool, and then move to hover the first image, the info is visible. edit: Second workaround: hover the thumb lower, eg. on top of the filename.

Ubuntu 15.1