Among the data that your pixel or URL has collected you may see a GoogleImageProxy user-agent. If you don't know what a user-agent is, you may want to read What is a user-agent? first.
The GoogleImageProxy user-agent is the user-agent that is tracked when you send mails to Gmail users. Gmail uses a proxy to retrieve and store images, including the tracking pixel. This causes the tracking pixel to track the proxy instead of the user itself. Gmail uses this to anonymize the retrieval of images. This prevents tracking pixels to accurately retrieve location data. Read more about the accuracy of location data in How accurate is the location data?