That all depends highly on the file size of your pictures. They can range from huge RAW files from DSLR cameras to very tiny images from a small point-n-shoot compact camera. A fairly high resolution JPG file can be an average of 2mb. If a 1TB drive is completely empty, and assuming you can actually store 1tb of data on it (usually it's less than the total drive), you can save 500,000 photos that are 2mb each.