.ATTR File Extension
What is an ATTR file?
File created by Apple iPhoto, an image editor and organizer program; contains an image's data; created to accompany an image whose attributes have been edited.
Files are located in the subfolders of the iPhoto program.
NOTE: Used by iPhoto 2 and earlier installments, not used by iPhoto 4 and later. iPhoto was discontinued and replaced by Photos in 2015.