Image log lets you upload a JPEG image (which is smaller than 800kB), and monitor the people who access it.
The user's IP, request string, referrer, user-agent, and the request time, are all logged. When an image is uploaded two links are given; the normal link to the image, and the link to the image-log which lets you view the details of everyone who viewed the image.
Please link to this if you find it useful, so that it doesn't have to be rewritten constantly.
Download the code here. Contact the author here if you notice a bug.