You can add a main photo and a small gallery. They're the first thing a venue sees, and they do more work than the bio.
Use photos you have the right to use. If a photographer took them, make sure you're allowed to. The same goes for photos of other members of your act: they need to be happy with it.
Agencies may use your photos and act name to book you: showing you to venues, including you in shortlists and offers. That's what they're there for.
They can't use them in their own advertising, posters or social media without asking you separately. If an agency wants that, it's a conversation to have with them directly.
You can change or remove photos at any time from your profile.