Index key value by which records in the image data file are looked up by the Platform Server.
Typically, a short and unique image identifier, such as a SKU number, possibly with some sort of image suffix, if a SKU has multiple images. May also be a more complex string that looks more like a file path, to support easy retro-fitting of web sites with Image Serving.
Text string. Required. Primary index key for the image data table. Each catalog::Id value must be unique within the table.