What an absolutely AWESOME idea!
I might also add that it might be nice to add his name, branch, rank, and serial number and of course "Made with Love" somewhere, just in case it would get separated from him. It could then always find it's way back home to him.
It would also be noted that bright fabrics probably shouldn't be used. I would use camo or camo type colors, greens, beige, tans, dark blues, greys, etc for the fabric opposite the pictures. The white fabric is sure not to stay white, so you could also lightly tea stain the white printing fabric for the photo side.
This could be used as a scarf, face wind break, etc. oh how cool this is! You could also combine this with some helmet and neck coolers in matching or coordinating fabrics.
Thank you so much for sharing this wonderful keepsake of and from home to help get them through until they return.
Thoughts and prayers to your son-in-law and all of our military personnel doing their part for all of us in such a difficult time.
Pam M