My wife love's calendars. I tend to use electronic myself but we have big calendar in our kitchen for household use, she has a desk calendar. I have calendar's with pictures on them myself. I think the market is still there but the competition is fierce - they are already sold everywhere. Good luck!
Right, calendar season starts in August. Thats when all the book stores have them and good titles are sold out by end September. January and February are also good month for calendar sales, but then only with highly discounted prices.
In several of my private niche interests there exists many non-profit B to C firms marketing them as a fund raising mechanism.
So this idea has a B to B as well as a B to C market potential. Some non-profits lack the ability to assemble content (photos) and forward them to printers. A potential web app aka a single page PDF for a fee?
I still print out a paper calender. It's just easier writing stuff down sometimes, plus it's right there in your face to remind you of stuff. Would I buy one? It's not really on my priority list. Like most things, I think the subject-matter would be imperative. Flowers and stuff... No. Done to death. But very niche subjects that appeal to a very specific group? Maybe. If you can reach that group, and maybe do some kind of special subject that you could turn viral. I think there's always room for a new spin on stuff.