Choose the caption bubble to begin. If you want to upload a custom bubble or alternative image then submit the caption first, then edit the comment and attach a "Place img". Once the image is approved you can use it by editing the caption again.
It actually surprised me how quiet it was in Central Park... just walk 50 meters into it and you'd practically hear none of the street noise, and could just listen to the calm breeze in the trees... Now I know why people value it so highly :)
Drizzt^
