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.
I was first thinking this pic was not going to be as good as it should be, but when I looked it afterthat, I thought to myself, it's going to be ok, now I'm quite happy of it :]
laughed my ass off