I am most likely not able to find this option, or at least missing already submitted feature request (I did try to search for one before postig here).
However I was very surprised to see that it is not possible to add a photo to an activity!!?? Please somebody tell me I am mistaken.
I have been using Garmin Connect for about 3 months now and do not normally add photos to my workouts, but today was the first time I was out with my newly purchased new road bike. On this occasion I thought it worth to add a picture to my Activity and was really very surprised not to be able to find this option!!!