After viewing something like this, you have a choice of reaction. You can choose to be offended, or you can choose to find humor in it, or to simply find it neutral.
Your reaction may or may not affect the other person, although it is likely that if you choose to be offended, he will choose to keep offending you. But even disregarding your reaction's effect on him, there is the issue of your own well being to consider? Which reaction is best for you?
The picture has been sent; the incident is now in the past. The past does not change, regardless of your reaction. If you cannot influence these things, why wouldn't you choose a response that maximizes your own happiness? Smile, find the humor.
It is possible that the photo triggered some feeling of inadequacy--don't get defensive (to him, or me)! I can certainly understand that. Perhaps he was implying that you ride a bike because you can't afford a car, or something. I drive a 25 year old car, and a beat up 20 year old cheap hybrid bike. So anybody who looks at me and thinks I'm, well, cheap? They're kinda hitting close to the mark. I do sympathize. I have often dreamt of the shiny new car, or the shiny new bike.
But these are all choices. I could afford a new car. I could afford a new bike. So could you, either now, or eventually--someday, given discipline. But both my car and my bike are adequate for my needs, and there is frankly other things I'd rather be doing with that money. If I thought otherwise, I'd buy the new stuff. So is is perhaps unfortunate that I do not have the shiny new things that my peers have, but I'm quite happy with the way I'm spending my money thus far.
Again, though--this is again talking about *your* choices. You get to choose! You may not like all the choices you get, but you're still allowed to do whatever you can to make your choices work out. It may indeed turn out that your priorities are different than those of others--surprise, surprise. Likewise, his priorities appear to not value bicycling, or even health. That is perhaps unfortunate, but it is his decision to make.
My apologies if the veering off track was not quite applicable. It's just been on my mind lately when I hear about some of these slights. Best of luck in dealing with your difficult coworker.