Looks to me like FIVE pallets. The one in the back looks like a double stack. One in the foreground, two behind that and then a single double stack in the back. Look at the wood pallets themselves, not what is on them. It looks like the one in the back has had the plastic wrap partially pulled down, probably to grab a box off the top or examine contents.
When you load a truck, you put the heavier stuff over the axles, you have to distribute the load correctly when you load the trailer.