There are a lot of applications that can help you back up photos from your phone, but many do not give you the freedoms you expect from free software. I believe GUI-based apps make this more difficult than it needs to be. I have decided that I will start using command line tools for this from now on. Here is the magic sauce:
jmtpfs ~/mnt
rsync -vrt ~/mnt/Internal\ shared\ storage/DCIM/Camera/ /mnt/backup/photos/phone
-vrt is verbose, recursive, and include timestamps. rsync will use
timestamps/file sizes to decide if it needs to recopy files. The first
run wrote this at the end:
sent 20,719,784,884 bytes received 23,956 bytes 30,582,743.68 bytes/sec
total size is 20,714,634,422 speedup is 1.00
The second invocation returned immediately:
$ rsync -vrt ~/mnt/Internal\ shared\ storage/DCIM/Camera/ /mnt/backup/photos/phone
sending incremental file list
sent 44,653 bytes received 63 bytes 29,810.67 bytes/sec
total size is 20,714,634,422 speedup is 463,248.82
Unmount with fusermount -u ~/mnt. Link to jmtpfs.