Currently, you can't directly use the blob_id as the image_url in NFT contracts for Sui. Instead, you need to set the image_url to the URL of an aggregator along with the blob_id. For example, you can provide a URL like https://blobid.walrus/qwer5678…, which uses the blob ID to fetch the image through an aggregator system. One concern is if the aggregator's URL breaks or changes, you might need a function to update the NFT with a new URL. Alternatively, using an intermediary layer between the NFT and various aggregators could help ensure the image remains accessible.

It's not currently in the plans for Sui's system or marketplaces like SuiVision to automatically recognize and render images just from blob_ids directly. It seems placing the responsibility on other apps is the current way forward.