Yep, they're not real pretty, are they?? I agree that diet/nutrition are or at least have been a big factor. Those 'growth rings' indicate laminitis. What are you feeding him? How long have you had him? I would ensure he has a low sugar/starch diet(no grain, etc), gets constant access to low-grade hay and gets a *good* complete vit&min supp. In order to ensure his nutrition is well balanced - which depends on what he's getting out of feed & pasture too, a diet analysis program or service is well worth it, I believe(I'm a subscriber of a program/service called 'feedxl.com')
I wouldn't bother with pine tar & sealers & the likes, just ensure he gets a good soaking in water every day or 2 if you're in a really dry environment.
Trimming properly & regularly will make a big difference too - while the feet may still be weak for a while after diet changes, good trimming will remove the unhealthy stresses & allow the cracks to grow out. It's obvious that the feet are a little too long, but not so clear from that angle how severely (or otherwise) they're flared, high heeled, contracted, etc. Depending on those factors, the feet may need to be 'backed up' a fair bit too, and ensuring a strong 'mustang roll' looks like an absolute must. I would get the trimmer to show you how to do this, so you can keep it up in between trims.