Why do people say "already liked"?

[Wyl]

On Facebook I see people commenting on peoples pictures saying stuff like "already liked mate" I don't understand, can someone explain?

[shroud]

simple they saw that picture or other item earlier
posted by someone else
and they don't want to like the same photo 20 times a day

[rosani]

someone already like that why?

[Daniel]

Someone Probably Asked them to Like a Photo That They Already liked And There Letting that person Know That They Already Liked it

[girge]

If someone puts a status saying 'like for a like on your pp' or something like that and you like the status they will like your pp but If they have already liked it they will comment 'already liked'