Photos on my Mac not showing in iCloud / photo stream
A number of photos that are on my Mac (in the Photos app) are not showing up in iCloud. These appear to be photos I took with a dslr camera, not an Apple device. Could that be the problem? In any case, does anyone know how can I sync ALL photos on my Mac with iCloud, so that they all appear in my photo stream -- and do so without deleting any photos which are currently on my Mac / in my photo stream?
MacBook Pro, OS X Yosemite (10.10.5)