I'm going to be travelling in and out of the USA in the near future, and I'm not sure if I can do my tip on a US Visa Wavier Programme or I need a "proper" US Visa

I've been asked to do some event coverage in the USA with my camera (as they feel a Brit photographer as a different eye), and to sell prints. I will not be performing press duties, mearly doing photographs for people.

I hold a British Citizens passport. I will not be working for any press organisation... just myself.

I've checked the US Embassy website, but its as clear as mud.

Can I use US Visa Waiver Programme.. or is it time to get a proper US Visa?

thanks!