The little star icon on your photo means that you received a Guru's Pick.
The Guru's pick means that the challenge Guru voted for your photo - this results in 50 votes added to that photo.
It also means that your photo became eligible to be selected as a winner of the 'Guru's Top Pick' award in that challenge.
Your photo must be in the challenge (not swapped out) when the Guru gives their 'Guru's Top Pick' selection in order to be selected.