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You can't echo something, have it displayed, then remove it. Once the content has been sent to the browser for display it's there. Trying to stream content as a progress indicator is already questionable. It may or may not working depending on what kind of software / buffers are involved in the connection. If you want to progress indication then the ideal thing to do would be to run your tasks as background requests using fetch() and update a display with the progress information as they complete.

In general, images are best stored either on a filesystem or in a CDN like cloudfront or akamai. It's enticing to store them in a database that you are already using, but it's highly inefficient. Blob storage in databases is expensive considering that you must query the result from the database in order to then return it to the client. What most people do instead is have a table that stores a path to the image, so that you can have the best of both worlds.