Furthermore the "Add picture" control stores things as a blob no matter what.
If you hook PowerApps to flow and try and use the image(s) the blob URL is sent as a string, and therefore cannot be processed at the flow end. Flow can only handle dataURI encoded strings.
Now there are a couple of ways around this depending on your perspective. One easy thing to do would be to provide a function that allows a local blob item to be converted to a dataURI formatted string - hence the idea of a BlobtoURI function. This would mean I can deploy PowerApps and have the ability to work with images just using flow and not having to resort to writing a custom API or Azure fucntion.
While I recogmise that a good solution might be for the flow team to support formdata from PowerApps and not just a string, I beleive the method I present here is simpler, has no UI impacts and is unlikely to create regression issues as it is simple adding a function.
This thread is a key to understanding this issue...