My law enforcement relatives have made us- as an entire family- very cautious about online identity issues. I am pretty sure that if a winner asked the sponsoring organization not to publish a photo out of privacy concerns, they would honor that. So that- in and of itself- should not be a reason to avoid these scholarships.
The bigger issue IMHO is that the odds of winning the big ones are miniscule and the amount of time they take is relatively large. So you need to figure out if the payout is worth it. They sound very enticing- but do you realize how many kids apply???