how can I move an image from my MacBook air photos into an assignment to turn in with it appearing as an image, not a jpg number encoding
I would recommend the best option is to click the Photo you would like to use in the Photos app on your MacBook Air, then click File --> Export.
Accept the defaults and then save the file to your Desktop (or Downloads folder, somewhere easy for you to remember and find it).
Following that, jump into Canvas and when you go to submit the assignment, in the file upload area, navigate to the place you stored the photo, select it and upload.
Please let me know how you go with this, or if you have any issues.
Hope that helps!
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