Since macOS Sierra was released by Apple, we have had some reports of the native installer failing after the "Downloading" progress bar completes. We are researching this behavior change in Sierra.
As a workaround, drag the Bay Photo app file from the disk image (the opened .dmg file) and drop it into the Applications folder. Then double click and run the .app file from there to install.
For a visual example of how to do this, watch the video below: