The wiki pages get created in their own Git repository and the image files are also added there. You can browse the repos from within DevOps at; https://dev.azure.com/MyOrganisation/MyProject/_git/MyProject.wiki
The markdown path for the image should begin /.attachments/ and make sure if you are adding dimension you use =500x and not =500 if you exclude the height e.g.
For more info, click here.

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