iphone 5 camera dead pixel?

Hello!

I have got a problem with my iPhone 5 back camera. It shows a dark spot on all pictures, so basically I have to re-work every single image afterwards.

I went to the apple store but they told me it's a dead pixel which is caused by taking too many pictures or pictures against the sun. I got the phone from my dad who never took pictures, so it doesn't seem very probable to me.

Unfortunately, it is older than the 1 year warranty, so they don't replace it.

Is this really a dead pixel (the shape is not straight, it's rather blurry)?

Can it be repaired somehow?

Thanks