consider using defocus detection algorithm

[xinario]

Came across this lib from https://www.birme.net/. Seems like it was used for focal detection there. I also found you are developing machine learning based algorithms (better looking for papers on saliency detection) but traditional image processing based method might be worth considering. Spearking of this, I'm shamelessly advocating my own work which works very well in the pre-deep learning time and is lighting fast.
https://github.com/xinario/defocus_segmentation