BitTorrent Sync is a nice app to synchronize folders with your phone via your local WiFi without having to trust a central third party server. However, I ran into a little problem when trying to sync with my Android phone. I wanted to write the data to the phone’s SD card and have it appear in the gallery. This is possible, but not straight-forward. Here is how it is done.
First open the “File Manager” on your phone, select “All Files”, “SD card”, “Android”, “media” (create those folders if they do not exist). Then you create a new folder with the name “com.bittorrent.sync”.
The next step is to install Sync from the Play Store, open Sync and go to the “Settings”. In the “Advanced” settings you find an option for the “Default folder location”. Set it to “/storage/external_SD/Android/media/com.bittorrent.sync”. You might have to use the up arrow in the top right repeatedly to go to a higher level in the folder hierarchy first.
Finally, all that is left to do is to add the folder you want to sync as usual. They now should sync to the SD card and picture files should appear in the Gallery.
To explain the background a little bit: Android apps are only allowed to write to specific folder on the SD card belonging to them. If you try to select another folder, you will get an error message and the option to go to the application’s folder. This, however, will usually be “data/application_folder” which is not scanned for media files. In contrast, “media/applicaiton_folder” is also writeable by the application and will be scanned for media files but has to be created manually as explained here.