iPhone: Camera image effects
When you capture a still image or video, a purple (or other color) flare, haze, or spot may appear from out-of-scene bright light sources. Most small cameras, including those in your iPhone, may exhibit flare at the edge of the frame when you capture an image with out-of-scene light sources. This happens if the light is at an angle (usually outside the field of view) and reflects off the surfaces inside the camera module onto the camera sensor.
To minimize or eliminate the effect, move the camera slightly to change the position at which the bright light enters the lens, or shield the lens with your hand.
Please see these troubleshooting steps for more information.