This is not a Tagalog word but it does appear in a lot in tweets and Facebook posts of Filipinos.
CTTO is short for “credit to the owner.” It’s a shorthand way for a person to admit that the photo being posted was not taken by them (they don’t own it), but by someone else. Oftentimes though, the credit is not actually given (in the original sense of the term) because the owner is not named.
For young kids these days, the use of CTTO absolves one of the responsibility to give credit (in the original sense of the term).
This concept is also rampant among the younger generation on Youtube where simply stating “I do not own this video.” in the description box makes them feel it is ok to post a video they do not own.
Adults who grew up with the “older” concept of copyright may find this very bewildering but that’s how things are now.
misspelling: ccto

