Hello singhmaan7,
Thank you for the question. I found an article that addresses a purple spot that might appear when taking pictures with the iPhone camera:
Symptoms
A purplish or other colored flare, haze, or spot is imaged from out-of-scene bright light sources during still image or video capture.
Resolution
Most small cameras, including those in every generation of iPhone, may exhibit some form of flare at the edge of the frame when capturing an image with out-of-scene light sources. This can happen when a light source is positioned at an angle (usually just outside the field of view) so that it causes a reflection off the surfaces inside the camera module and onto the camera sensor. Moving the camera slightly to change the position at which the bright light is entering the lens, or shielding the lens with your hand, should minimize or eliminate the effect.
You can find the full article here:
iPhone: Camera image effects
http://support.apple.com/kb/TS4436
Thank you for using Apple Support Communities.
Best,
Sheila M.