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 went sailing and scubadiving around the Whitsundays Nov last year. Fantastic place to be and the beaches are amazing. The sand is something like 95% silicate and is so fine it makes a strange squelching noise when you step on it ...
The colours of the coral and the fish is amazing ... I got within 3 feet or so of a Manta ... massive things that glide through the water effortlessly ..
Select "Place Img", then browse to the picture, the simply time [img1] and [img2] and [img3] and so on according to how many pictures you upload. :) the [imgX] will be replaced by the images according to the order they were uploaded with.
I'm not a big fan of src'ing images from other sites so there's no option for it here. You have to upload the image basically - do this by editing the comment and attaching a 'Place Img' file like netrex says.