This is one thing the horizontal section doesn't support yet. You have to have fixed width/height per each item.
This is not a simple matter for the same reason why dealing with vertical scrolls was not a simple issue.
In fact this is not a problem unique to Jasonette (like the tableview scrolling issues) If you look at most other apps that support horizontally scrolling components, most of them have equal width per unit for this reason.
The most frequent trick people use for this type of situation is to crop the images so that they fit into each unit. And when people click on them they will be directed to the actual view where it shows the original version, etc.
I hope this will be supported somewhere down the road, but for now above is the only option.