You open min.us, you drag and drop an image from your file manager / desktop / whatever, and you're done. Period. Brilliant.
Genius resides in designing things that are simple, or at least apparently simple. The success of Google Search with users does not only rely on its search algorithms and implementations, but also on the extreme simplicity and consistence of its user interface (at least as far as the landing page is concerned). Sure, nowadays, you'd think "why would I make a search page look any different from that ?", but back in the days, all the other search sites had very complex user interfaces (at least as far as I remember).