ODK Collect v1.29 is now in beta and it no longer registers media attached to form instances in device-wide galleries. We believe this is the best behavior for most contexts and matches most modern apps that are not dedicated to media capture.
We explored this a bit and as far as I can tell, the prior behavior would not have automatically helped with this. That is, you'd still need to e.g. open the Dropbox app, select images that had been captured with Collect, and add them to a Dropbox folder. My recommendation for that kind of need would be to use the device camera app to capture images and then browse to select them from Collect. We can include this in documentation as well.
We're very interested in hearing from anyone who might have a workflow that interacts with this change.