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Learnability: it's difficult to understand how to get feedback about your drawing from the system. User may not be able to understand that he should make photo after he drew the picture. Also there is no feedback from the system on your actions.
Efficiency: the user doesn't have an account and the app doesn't store the history of previous pictures. So, the user can't see his progress over days or months.
Safety: no possibility of cancel actions or making undo. If user made a mistake he won't be able to correct it.
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