IPhone : Image cache and management on iOS

I have a json file which it's body is an image in form of binary(NSData). I download it and convert it to an image using:

    [cell.imgPhoto setImage:[UIImage imageWithData:imageData]];

And load it to an image view into a cell. I have two major problem. First is downloading an image several times and second is caching. I can't change server side codes and I have to work with that! I emphasize on downloading in form of json and it's body is an image.

How can I do it or is there any component to automate it for me?