Do you have some poor resolution images? Perhaps they came from scans of bad images or the photographer (we are not pointing fingers at you) wasn't very good on that day?
There is an online service for enhancing photos that uses artificial intelligence that is very good - not perfect - but can improve a certain class of images. This type of enhancement should help with better face detection and recognition. It is offered by MyHeritage.com - the genealogy site. It is free to use for single images - give it a spin.
In fact, now there are multiple services using advanced Artificial Intelligence (AI) software to enhance, enlarge, and even remove backgrounds from images. Here are a few examples:
The PicWish service seems to generate really solid results.