I followed your posting about Exporting from iPhoto.
File-> Export and the window pops up, Export, and I set it up as that posting said, even changing the Kind to PNG for one attempt and a second one with the Kind JPEG which my photos are taken in. Size (Custom), Max (height), all settings as that posting had them.
In iPhoto after importing my photos into the computer I highlight the photo I want to work with, click on info. On the right side you have the camera details about the photo e.g. ISO etc. Below that is IMG No then date and time taken. Under that is a window which says, add a description, and it is here where I put the information about the photo, where it was taken etc., this is what I refers to as caption.
Hope this makes sense to you.