Copyright is invested in the creator of the work, for the life of the work and 50 years after. Clauses, statements and warnings of the type that Instagram publish are just nonsense (you will also come across these statements in photographic competitions) and any court of law will prove that. There was a stir here in Australia about Instagram's policy. Not surprisingly many people discontinued using Instagram. Reassignment of copyright is a legal process that nets big money for the creator; effectively you are giving your work away for a fee so that somebody else can claim ownership to it and use it as you see fit (Getty Images is unique in that creator copyright remains with the photographer, yet Getty licences the work to produce income; there are a few photographers here in Australia doing very well with Getty). In Australia practicing artists are guided by the National Association for the Visual Arts that examines and dissects any alterations to central copyright laws; to my knowledge, the only trouble we've seen recently is the statements published by Instagram and competition organisers etc that copyright is owned by them once work is entered. It's not. Plain and simple.