Same here. Playing since Easter and never had a photo. Suddenly I got three in two weeks. Strange. The one villager who is so in love with my character just won't give me a photo! I don't know how I'm going to get it!
Alot of it is just luck, the percentage chance each time you gift is very low! Bangle was one of the last of my villagers at high enough level to give me her photo, even though she is my original peppy. Make sure you are following the gifting guides, which have changed a couple times since the game came out. I had a spell of getting no pictures for a month, and it turned out i had missed that giving one wrapped fruit no longer works. After i started gifting the right kind of gifts I got 5-6 pictures in one week (they were all just waiting to give me their pictures once i got my act together i guess). Things like giving clothes don't get you the photos, and I don't think sending letters does anything either. yuecrossing's guide, which someone mentioned above is great, and @Sharksheep is an expert at this stuff.
I used to gift every day before the new update. That gave me 6ish villager pictures. Since this, I've sort of stopped gifting and haven't earned one since. It's pretty tough imo. Good luck!
You should check this thread out. I found it very helpful. It also explains how to get multiple copies of the picture. You need to gift them about 64 times before you can get another one again.