I'll have to add that to the terms and the faq - I'm using google apps to handle the email. The app issues a delete immediately after processing. Right now I'm clearing out the trash folder (edit: sorry the sent folder) in the google account about every day or so.
What kind of assurances would you like? If I implement accounts, would you be comfortable with storage? Would you want to be able to choose on a per-picture basis?
I once worked in the information security group at a large insurance company, and they prohibited their employees from using, e.g., AltaVista Babelfish, lest they mistakenly release confidential information via the translation tool. Instead, they wanted employees to use a local desktop-based translation tool.
For all of the security measures that can be taken with sending data to web applications, "never sending it at all" is very secure indeed, and in some arenas, the inconvenience may be worth it.
I no longer work with them, so I can only surmise. I never saw anyone using a tool like this, but it's a big company with many offices, and individual groups may well have bought their own local tools that weren't provided at the enterprise level. Would they buy a desktop version? If employees found it useful, I don't see why not.
They almost certainly would not use the web version, unless they could run it 100% internally on their intranet.
In my experience, most companies that have rigid security/compliance policies against using simple web services like babelfish, google translate, etc. also have rigid purchasing departments that make it almost impossible to sell them a simple, inexpensive desktop app. They only buy "enterprise solutions" from "approved vendors". Now admittedly there can be a lot of money selling those "enterprise soutions", but it's hardly a low barrier to entry game. IMHO unless the OP wants to get into the business of selling labyrinthian "enterprise" software, he should probably just ignore companies who have compliance policies that would prevent them using simple online services.