Can I use a black and white photo for my Decouverte Pass?
The Navigo Découverte is a blank card. There is no pass until you add one and there are a lot of choices. The ND card must have your printed name in the space so designated. There is no specification that the required photo be in color, only that it be an original photo of the size 25mm x 30mm.
the photo can be black and white or color but must be a very clear head shot so there is no question who it is. I have made maybe a dozen NDs for ourselves and for family visitors and in the early years, I cut heads out of photos to get the right size. The more recent ones I cropped and sized on the computer and printed them on regular computer paper. There is a clear gummed flap that folds over the front of the card and the picture so there is no issue with paper quality of the photo -- just image quality.
There are photo booths in metros and RER stations if you don't bring photos, but I'd just bring your own. the agent if there is no line, may put the card together for you, but often just hands you the kid, with the pass loaded and you assemble it yourself. It is not valid till assembled (It will 'work' but it won't pass inspection if you are stopped)
As an option (if you have a smart phone), skip the pass and download the "Bonjour RATP" app so you can set up Navigo and use your phone to access public transportation. You can purchase using ApplePay (or the equivalent) and, once it's set up, it works very smoothly. App also makes navigating metro and buses much smoother.