Source: (MUFON case 84702)
A variety of images reported as "UFO"zm show what looks like a glowing disk with some dots on it. These basically look like lens flares, but the dot patterns are unusual, as they vary from irregular, regular, or or semiregular patterns. However they still look very two dimensional - they don't seem to curve around the "orb". Here's a collection of similar images all claimed as "UFOs"
What we are seeing here is a reflected image of the sun with the highlighted reflections of focus pixel.
Focus pixels like these first showed up in large numbers in Samsung Galaxy phones. As you can see in the close-up picture above it's a modification of some of the green pixel sensors. More fully called "passive autofocus phase detection pixels", or Phase Detection AutoFocus (PDAF) pixels. It works by shielding pairs (or paired groups) of pixel in such a way that by comparing the light between the two the camera can detect if the light hitting from two directions is in phase, and hence in focus.
It's complicated, but the simple fact is there's this irregular grid of pixels on many sensors.
And the pattern of the PDAF dots matches the patterns seen in lens flares
So essentially the image of the bright sun, shining in the lens, is reflected off the sensor. The masked PDAF pixels show up brighter due to the covering material (which is why they show up in the microscopic pixels, above). This pattern then reflects off one layer of the lense assembly and back on the sensor.
Put another way what we are seeing is the image of the sun as it is projected onto the sensor. You'd see the same thing if you could somehow get a tiny camera inside the phone camera.
These dotted images are going to vary with camera because of different sensors (not all have PDAF), and different lens assemblies. Double reflections can be caused by additional layers of glass, like lens protectors, or may be the result of shooting through a window.
These image might become less common in the future, as Samsung has phased out the PDAF array with a new technology in the Galaxy S7, Dual Pixel Autofocus which eliminates the need to mask pixels as it uses ALL the pixels by having two sensors per pixel. See:
The majority of the images seen so far seem to be from Galaxy S5 or S6 phones. S7 phones will make an orb, but with no dots. I've not seen it on an iPhone.