Recommended Best Practice: this tutorial on the focused use of twitter by a presenter is a great way to close the gap between those tweeting at your presentation and what you're presenting on.
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is a Web 2.0 styled editor having different sections for different functions. The tutorial is not of explanatory kind. The user has to have a fair idea of working on photo editors. It is definitely not for beginners. Registering is required to save your work, hence mandatory. There are a few legal hassles also.