Camera photos missing? Replaced with android icon

[DCarrollUSMC]

I had a few photos on my phone that were taken with my phone's camera. For a while they showed up normally in my gallery and in file managers. All of a sudden today I wanted to show a friend the pictures but noticed they are gone from my file manager and gallery. They have been replaced by android icons. Any idea what could have happened to my pics and if I can get them back? Sorry if I haven't included enough info.

 

[DCarrollUSMC]

Update: There is a directory on my sd card called LOST.DIR. I have learned that these are files that have become corrupted. I'm curious how to recover these images.