The archivist says sure we have the mosaic and we'll make you a copy. But upon examining the delivered copy, the messenger's heart sinks again. We really should stop accepting these compressed mosaics, he thinks to himself, otherwise people will start doubting we are really serous about preserving mosaics. Now like our Greek friends, you know why it is important to save an original copy of a digital photo using a non-lossy compression method. This isn't always possible given that most digital cameras today save images using the lossy JPEG compression.
Many newer cameras have an option to save images without using compression.
Of course, the technical people will eventually solve this problem but not after millions of compressed images have been made. You also know why images saved with lossy compression are unacceptable for building photo archives. Well, if you're carrying a heavy load of tiles over those steep, narrow dirt paths through the Greek mountains you would understand the need to lighten the load considerably. Spend much time waiting for a digital photograph to download over the network and you'll understand why JPEG compressed images are the standard method of transferring photographic quality images online. They have good enough quality that most people don't notice any imperfections and they download quick enough that most people do not get impatient waiting.