I realise the rules might be different in different places, but assuming they’re not so significantly different as to make this question meaningless…
Is it considered littering if a person picks up an item of litter (perhaps mistaking it for something valuable), then drops it again?
If not, how about if they pick it up and take it home, then return to the same spot the next day and drop it again?
And if the answers to the two questions are different, why?