@JohnMorris3
We don't use Scantron, but I'm familiar with the Canvas side of things. You didn't link to any of the other discussions, so I apologize if I end up repeating what was said in those.
In Canvas, the gradebook is a way of organizing and managing submissions. When you say that you want to upload the comments into the gradebook, in Canvas parlance, that means placing them into a submission.
That means that if you put the Scantron comments into Canvas submissions that students are going to be able to see their comments. I don't know if that's an issue or not, just letting you know.
There are submission comments, which is a textbox -- as of last week it now supports limited HTML -- where you can leave text messages. I don't suppose the Scantron supports OCR for handwriting and that you want the actual image instead of the OCR text, so that's not particularly helpful.
There is no way to attach an image through the partial Rich Content Editor (RCE), nor is there a way to edit the HTML with the RCE. I have not tested to see whether it supports other HTML through the API. My guess is that it does because the implementation of the partial RCE was kind of haphazard and not well implemented across all of the Canvas systems. If it supported HTML images, then you could host the images somewhere else and link to them from within the submission comments. Prior to a week ago, you could include the link to the image that was stored somewhere else. That's not a secure mechanism, as anyone with the link would be able to read the comments, but it would allow students to see what their comments were by following the link.
There is also the ability to attach files to the submission comments. This is going to allow you to upload an image (PNG, PDF, JPG, etc) of the scanned comments. However, those are going to be visible to the student and sent to the student as a submission comment. That is, each student gets a copy of their comments sent to them automatically. That could be problematic if the comments happen to be answers to questions that you don't want to get out.
A second approach is to create a custom column in the gradebook. These have the benefit of not being visible to the students. They have the downside of not being associated with the assignment. Typically, custom columns are not used for assignments, but for other housekeeping things. They might contain a student's nickname, that they have accommodations, or other notes for the teacher. The major downside of this, which probably renders it useless, is that it is expecting a string for the content and you cannot attach an image. It doesn't support HTML, so you could provide a link to the comments that were stored somewhere else, but it wouldn't be an active link or something that would be visible directly from within Canvas.
All of those methods suppose that there is just a single comment per Scantron form. I don't know if that's how it works or not.
One way that I can think of that will address most of the issues, including potential ones like not allowing students to see the comments, is to create a quiz for the assignment. Within that quiz, you create a question for each comment, this allows for more than one comment per assignment if needed. You set the security on the quiz to be whatever you need -- allow the students or don't allow the students -- to see their response. The question itself can be a file-upload question or an essay question.
Now comes the tricky part.
If you create a file-upload question, then you could take the quiz as the student and upload the Scantron comments to those questions. However, if you are masquerading as the student, then the upload will go into their submissions and they will be able to see it. Also, a file-upload question is not viewable from within Canvas -- it has to be downloaded to be viewed. That severely limits its usefulness.
The other way is to create an essay question. Here, you would upload the comments into the course files rather than the student submissions. This prevents students from seeing them unless you share the results of the quiz. You then take the quiz as the student and embed an image in their essay response. This is untested on my part -- whether a student can submit a file from the course files that isn't available to them. But if they can, then the teacher would be able to see it. Since it's uploaded to the course files, it wouldn't count against the student like it would if they were trying to embed an image directly. This also means that you won't run into quota issues for students.
Taking a quiz as someone else is not a trivial thing to do. Grading quizzes and leaving comments is a much easier task.
There is another possibility that is a hybrid of the last two. You could make a quiz with any type of question. It could be a true/false question or multiple choice or whatever. The students aren't actually going take the quiz, so it doesn't matter. The question might be "Student Comments" or, if you need multiple comments per Scantron, "Comment 1", "Comment 2", etc. You still upload the Scantron comment images into the course files within Canvas. Set the protection on them so that students cannot see them if you like. Then, as a comment to the quiz question, you put the link to the file. The files won't be visible from within Canvas, they will have to select the link, right click, and open it.
I didn't go into great detail on any of those because I'm not sure if any will meet your needs. In all my API usage, I've never taken a quiz through the API and that route would probably be my last choice. I'm assuming that you want the comments associated with the assignment and that the students should see a score for the assignment.
