Sort:  

RAID4 is needed to put the picture together from the 3 files. https://en.wikipedia.org/wiki/Standard_RAID_levels

Usually you include a parity disk, that’s why you actually use RAID system. In case a disk fails you can reconstruct it with the parity disk. However for this challenge I wanted to keep it a less complex and not include the parity disk

I know what RAID4 is but I couldn't make the connection, very smart way to hint the picture creation!