Hi Editors

I recently stumbled upon an excellent video, promoting an event between two elite boxers. Now, there is one effect in the video that I would like to use in my own edits, yet I am unaware as to how I can achieve it.

The effects occurs during 0:42 and 0:50 in the video below, and it is a "flashing image" style effect.

I suspect that it is just a very good use of overlays but would anyone be able to assist me or give me advice on how to achieve this effect..

Thanks for any help.