Take photos at your lfs with their permission. Ask people on this forum to donate/release their personal photos to you. You could send them a photo release form via email. Electronically sign it and return it.
It'd be cool if the owners of the forum could export the data and make their own app. It'd be a semi easy way to make some extra cash and I know I'd pay even 3 to 5 bucks for a plant database that was updated and maintained. The hardest part would be trying to link an app to the existing content so that the process was simple and didn't involve extra work. I'd imagine that would involve some level of change in terms of how the data is entered currently but I don't do web design anymore or know anything about apps
You can have a feature in the app where people can take photos with their phone or iPad and upload it straight to the server for that plant. Let the users do the work.
That's really smart! You'd still need to have someone behave as a moderator though and confirm that the plant pics are accurate. And then we'd be back to monetizing the app unless you could find volunteers.