There are apps that will name the file based on the EXIF data (the metadata recorded on the file, which includes the location if you have the camera app set to save the picture with location data). Some of them can be let loose on an entire folder and told to add the date, time, location, whatever EXIF data you want, to every file name. (The only one I use timestamps the picture itself - it puts the date and time in the corner of the picture, but there are many others in the Play Store.)