Is this true about low-light/one photon at-a-time double-slit interference? I've consistently noticed in pictures of double-slit interference when very low-light or one photon at-a-time is used, that there's lots of "stray" photons detected in the areas of destructive interference.  That is to say, the pattern still emerges, but less "cleanly" than one might expect. 
On the other hand, from all the representations I've seen, it's my understanding that in the original "normal intensity light" version of the double-slit, the areas of destructive interference can be made to at least appear completely devoid of light.
I'm aware that the difference might have an easy explanation if it's true. But that's my question...is it true? Have you noticed the difference that I speak of, or am I just imagining things?
 A: The key is in your words "to ... appear".   I believe that it's a perceptual issue with how your brain processes the two kinds of images:  a smooth rendering or a pixelated rendering.  
There is another possibility.  In order to be sensitive to single photons, the detector is also going to be sensitive to very low-level noise.  An image taken with a bright source won't have that problem; the signal of interest would overwhelm the noise.  
I rather believe that the issue is perceptual, but either way the effect does not contradict our understanding of what's going on.
A: It's an issue of contrast; in the classical wave experiment there is plenty of data, and the contrast between the peaks and valleys is very clear; but when you are counting one-by-one the pixelation remains obvious. 
Pixelation can be reduced by (a) more gray levels in each pixel, and (b) more pixels per unit of area.  You can simulate this by taking off your glasses and standing way back!
In my electron diffraction experiments (not shown here) the contrast became comparable when the aggregate electron counts were similar: short exposure times for a large number of electrons per pulse, vs long exposure times when there were only a few electrons per pulse. The same applies for photons, IMHO. 
The images here are borrowed from the Wikipedia article on the Double-slit Experiment; this one shows single electron interference patterns, the same experiment at different time steps.

A: You can get it as "clean" as you want - use sensors that only respond to a narrow wavelength (eg something so unlikely that it almost must be from your source...not IR for example!), set up your experiment so that the source will, statistically, emit a single photon every day or two to avoid the possibility that you're getting interference from the source "double tapping" the target, and so on.  Thing is, you can still, in principle get "noise" in the dark area. This is the nature of quantum mechanics. Unless you can set up your experiment to guarantee an absolutely zero probability of a photon striking the "dark area" then you will, given long enough, have the odd hit in the dark area. I'm not actually sure if this setup is possible - but what you can do is set it up so that you get a 5-sigma (or arbitrarily higher) chance of ensuring a dark area stays dark over any given timescale.
