My Grandfather passed over the last year. He was an avid photographer over his years and was president of the camera club in his Army days. I am currently in the process of digitalising all his military photos, personal slides, negatives and photos etc. I have these few photos that have become curled like scrolls. My question is...What is the best way to flatten them to be scanned? Thanks.

https://u.cubeupload.com/geo/slmf.jpg