Not all photos showing up in Photostream

Since upgrading my Iphones, MacBook and Imac and using Photo Stream, I am puzzled as to why only some photos show up in each device. Yesterday I took about 25 pics with my Iphone. When I got home, I noticed that none are showing up on the Ipad, and only some are showing up on the other iphone and MacBook. All the settings on each seem to be the same. Thanks for any help.

Bill