Steve has a Samsung Galaxy S4, but he's having trouble with the external microSD card causing the phone not to see his images. Leo says that there's a bug in the camera firmware of the GS4, when it comes to saving to the SD card. Leo says there's a firmware upgrade that addresses the issue. Android and SD cards have always been a mixed bag, and a necessary evil. This is why Leo saves to internal storage and uploads directly to DropBox to backup.
Another option could be that the card is corrupted. He can try another one, but save locally and back up to the cloud until Samsung figures out what's wrong with that camera. Leo also installed the Google Experience Camera and gallery, which he can get from XDA Developers.