For parents involved with the school council
As a member of the school council, my job was to organize the year-end family parties. Based on my experience, here are 10 cool ideas for photo ops during a fair. They speak for themselves but you'll find the links to their source on my Pinterest board titled: School Fairs: Photo ops. I also recommend you check my School Party & Fair & Fundraising board.
It can simply be a free activity within the fair, encouraging family to share it on the social media of your choice. If you choose to make it a fundraising activity, here are some suggestions:
1) You could charge a small fee for the privilege of using an ambitious decor.
2) People can pay for the right to take their photo with a special person (costumed principal, local celebrity or... a cute dog)
3) A volunteer could be the official photographer with a decent camera and take photos of people who make a small donation. Special props or decor could be used. Another volunteer would note the email address to send the digital photo to the donor with some detail about his/her clothing (in chronological order, so the photographer can match the photo with the right email).