"The lie occurs where the image ends."
exactly. The camera simply captures the image it sees. The lie occurs afterwards. If you argue that since the camera cannot capture everything and is therefore lying by omission, then I would state your perception of that is true to you. My philosophy is different however and I do not think the camera is capable of manipulation (lying) of its own accord.
If you agree that the lie begins where the frame ends then you would also have to agree with the statement - A picture is a partial truth, right? And therefore, the statement "A picture is also a partial lie" must also be true. However, truth, like pregnancy, cannot be partial. You are either pregnant or you are not pregnant, you can't be "kinda pregnant". Similarly, unless a picture is the full truth in all respects, it must, by definition be a lie. Perhaps a lie we can all agree resembles the truth to one degree or another but it remains a lie nevertheless.
But taking this a step further, the lie also occurs in the viewing of the picture. Your experiences and your biases will force you to "see" any given photo differently than someone else. Take the so-called "Obama selfie" taken at Mandela's funeral. Many people who looked at it saw it in a variety of ways. Which, if any, were the truth. The answer is none of them. Because the picture was a lie to begin with hence all interpretations after that point will also be a lie. So even if you could achieve a "truthful" picture, it would necessarily become a lie by the actual making of the image. Much like the Heisenberg uncertainty principle - as soon as you click the shutter you have created a bias that has fundamentally falsified the image and hence rendered it a lie.