Here are my 2 cents:
First, I would recommend you to drop the "raise awareness" label. The word has been overused and some people is starting to react cynically toward it and the events that sport it. Don't take this as a "terrible idea don't do it" advice: it is still an attempt to raise awareness, after all but not calling it this way will help you to keep people open to your message.
Second, and most important, be positive. You may manage to echo some indignation on your public but it won't last. Although using some photos of mistreated bettas isn't bad, don't stop there: show them our world, let our joy diffuse towards them, make them want to own a betta the right way; cups and small plastic ornaments aren't for bettas because their awesomeness can be contained in such small space! If don't have the time for a presentation, record some videos and play them at your speech. Show them how bettas flare, how they greet their owners with happy dances when they are given the space to do so, how female betta also exist, and they can conform this cool things we call "the sororities"; how all those corys, loaches or platys can actually hang around in a tank that is also complemented with the flowing fins of a male betta and how many varieties they haven't seen like the halfmoon and the crown tails are also there to please their sense of aesthetics. At last, you could show them the awesome betta coupling and how the betta male is badass enough to court the female and also man enough to care for his offspring. These fish are a full bag of surprises in a small pack, and they are worthy of their respect.
(Phew. I actually got inspired while writing this post. Hope it helps)