use the right file name and photo description fields
When I transfer a Flickr photo with filename IMG_8508.JPG and title "Hulk. Punch! Toilet ..." https://flic.kr/p/8dtxHD to G+ I get a photo with filename field set to "Hulk. Punch! Toilet ..." and an empty caption - https://plus.google.com/u/0/photos/+AigarsMahinovs/albums/5992553435540618833/5993001684900791186
It would be better to use the title as caption and (if there is no real file name available) autogenerate a sequential file name in the set with some kind of set ID pre-pended. This is essential for when the users then click "Download" on an album they actually get sequential file names in the resulting zip file.
Oh and the downloaded files also have modification time set to midnight of january 1st of 2012 for some reason, while the photos were taken in 2010