Anyone with a background in computing would respond, "duh." The operating system maintains a file table which contains the addresses of pieces of data on the disk. Deleting a file just removed its file table entry, and in most cases leaves the data untouched. That's why data recovery software exists, and it's also how we have the "Trash" or "Recycle Bin". If you want the photos completely erased, you'll need to overwrite the data, which wastes time and write cycles...