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Completed tasks are shown in the list as checked off tasks, and the image of their completer is shown next to the task.
Analysis:
Learnability:
This design has good learnability. The to do list is simple and intuitive. Using checkboxes to complete tasks keeps external consistency, since it is likely users have used checkboxes in the past when using a to do list. Completing a task might need some figuring out, since it is not very clear you can upload an image to show off your work. This could be improved by changing the upload button into something more relatable.
Efficiency:
I think efficiency might be one of the few problems this design has. Although checking off a task is efficient and unobtrusive, the completion form requires an image. Creating a task seems simple enough, but it also requires an image. I think the time needed to upload images greatly reduces efficiency. Users need a camera for these things, which is a big requirement. Additionally,.once the user starts using the app, they may actually have to leave their computer to go take a picture and come back before continuing. This is not ideal and should be revisited.
Safety:
Safety is not a problem. All actions are recoverable. Completed tasks will remain in history, so even if one checks off an incorrect task, the user will be able to undo it. In essence, every action is undoable and the user does not need to worry they will ruin the experience.