This tool allows you to paste a IIIF Manifest URL into the box below and it will show you all of the Canvases which are present in that manifest. You can then click the Copy Image URL button if you want to get a link you can use in the Bodleian Manifest Editor.
If there are lots of canvases in the manifest you are using you can use the filter box to start typing the label of the canvas you are interested in.
You can find Manifests using the IIIF Guide.