Have you tried using the stack method? I was able to get all my villager's pics (besides the new ones) that way!
...I don't have a link to the thread describing it, but once you've reached max friendship, fill your inventory and gift the villagers from a stack of fruit (exotic or coconut, must be unwrapped!) They'll just take the top fruit and send you a thank-you gift in the mail, which has a decent chance of being their picture!
Seriously, I cannot recommend it enough. Not only does it give you a good shot of getting their pics (I don't believe they give them in exchange for gifts UNLESS you use it, because they only have a chance of sending it in the mail... it's weird) but it also keeps you from potentially messing up their houses with furniture or excess clothing.