Could you walk through the steps you use a little bit more?
2) Call RhoConnectClient.doSync() (DB snapshot #2)
3) At this point your rhoconnect server should receive a POST request (visible in the logs) and your store_blob method in your source adapter model should be executed.
4) Next you should see a GET request in the rhoconnect server logs as the client will download backend changes (your source adapter model query method should be executed). Make sure your query method updates the blob attribute (see the sample code here: http://docs.rhomobile.com/en/4.0.0/rhoconnect/blob-sync ) (DB snapshot #3)
5) Now your local copy of the record (make sure you fetch again from the database via the `find` method: http://docs.rhomobile.com/en/4.0.0/api/OrmModel#mfind ) should have a URL for 'image_uri' model property. This assumes you set it to a URL (i.e. http://example.com/mypicture.png) in your source adapter model's query method from step #4.
If you're using rhosimulator, you can create copies of the rhosimulator/db/syncdbuser.sqlite file where I mentioned DB snapshot #1, #2, #3, respectively. This will help with understanding what is going on at each stage of the blob sync process.