Question here. I've been gifting stuff Zucker each day for the past few weeks. However, he's not given me his photo.
The gifts need to be above a certain sell value, which I believe is 750 bells - not the price you’d buy something for, but the amount the nooklings pay you for it. So, for example, most clothing does not qualify and you cannot receive a photo in exchange (you still build friendship this way though).
3 wrapped coconuts/ pumpkins works or 2 wrapped non-native fruit, or 8 wrapped native fruits.
It generally takes about 4 weeks from when a villager moves in to when you can get a photo. But because RNG is involved, it could be longer.
If you are getting a higher percentage of floors and wallpaper as return gifts, I believe that is also a sign your friend score is going up.
Villagers can also give you their photo as a gift when they are visiting your house, or as a return gift on their birthday.
It seems to me to be less common but you can also get he photo as a reward for a treasure hunt or another favor you do for your villager.
Hope that helps, likely you are just having a bit of bad luck, so hang in there! Hope you get zucker’s photo soon!