Inspector
Nyuck, Nyuck, Nyuck!
I used to bring pallets home from work to salvage the wood and they were nailed together with glued and serrated nails. If the nail head was above the wood, like I see in the picture I would give them a hit with the hammer to help break the grip and use a long crowbar to pull it. Where they came through I cut the threads off a long bolt and drilled a hole a touch bigger in diameter than the nail and deep enough so that most of the nail was in the bolt. I could slide it over the bent nail to straighten it to approximately the way it was driven in and hit it with the hammer to get it moving. It won't buckle over like it does when hit with the hammer only. You can have a second bolt with a shorter hole to go further or just use the hammer from there and finish with a crowbar on the other side. The remaining ways have already been mentioned. I never heard of a de-nailer until I didn't have access to the pallets anymore. I do have a palm nailer now and would be tempted to try driving out the nails with it. Sure works good putting them in.
Pete
Pete