Phone resets when scroll through pictures ... does anyone know ..

I have been having the issue of scrolling through my pictures and my iPhone just stops, the screen goes black and then resets to where I have to unlock my iPhone again. Is this an on-going issue? I have hard rebooted my iPhone, and deleted several hundred pictures. I've gone from looking through all photos to months. Doing the months seems to help a bit but it will eventually lock up again and reset. Would anyone be able to offer suggestion on a work around?