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The computer then analyses the designs he has selected and gives him some sort of feedback about it, telling him about what tattoo genres he seems to like, and also (based on some weighted function) recommends tattoo artists he should look for based on the styles he likes and the distance from a specified location. This also means that there will be a database of tattoo artists, which includes their specialties, locations and preferences. By repeatedly browsing the different tattoos at random and seeing what sort of choices he likes, Jack learns a bit more about what sort of tattoo genre he likes, and can kick start his tattoo design process.
Learnability
The interface may be slightly challenging to learn because it may not be immediately obvious what to do at the beginning. However, I believe that the learning curve is shallow, because of the familiarity of drag and drop. I think the learnability of the gallery interface is also good because most people are immediately familiar with what can be done or what cannot be done with a gallery interface, and also drag and drop has become quite ubiquitous. Finally, there are not many buttons (mostly just the Analyze button), so the usage should be quite straightforward. As long as the interface is not cluttered and the instructions are clear, then the interface should be easy to learn how to use.
Efficiency
I believe that this interface should be quite efficient because there really isn't much for the user to do except to select the images he likes and to drag them to his sketchpad and analyze them. The simplicity of the layout should help also. There are also only two main modes of the interface - browsing, and analysis. This is easily toggled using the close button and the Analyse button, therefore I believe this interface is fairly efficient.
Safety
I believe that the interface is quite safe to use. There isn't anything difficult to go wrong, because it is simply not allowed by the interface. However, there can be two places where it might be unsafe.
1. Firstly, the user may erroneously drop something into the recycle bin and be unable to get it back. This can be made safer by adding an undo button, but there can only be so many history choices that can be saved.
2. Secondly, the user may accidentally hit the back button of his browser, and lose his chosen items. This can be solved using cookies in the browser, or if we implement a log-in feature where the user's selections can be saved immediately.