Every time a vacancy occurs the owner/landlord will have to evaluate the walls. It is always best to start a new tenant off with walls in perfect condition. This perfect condtion will help attract a better tenant and will also give a good starting point from which to evaluate the condition upon move out.
Whatever the condtion is at the start, it should be documented in writing, photographs probably will not help that much, and signed by both the landlord and the tenant. If the walls have new paint, write that down. If there are marks, write that.
Upon move out, you can go back to those original notes and compare to the current condition. If money has to be spent to bring the property back to original, the tenant may be held responsible to pay. They are entitled to normal wear and tear, so you should have a policy to depreciate the paint job, probably over 3-6 years. We lean on the nice guy side and use 3 years. If a tenant lives in the home for 1.5 years, they pay half of the cost to bring the walls back to original condition.
If you get into a dispute with the moved out tenant, you will have to convince a judge if they sue you.
With ongoing tenants, I would not repaint more often than about 6-10 years. It all depends on what you want to do in this area. I know I don't paint my walls more often than that.