Three different clocks

A frame can arrive in your browser now without showing a scene captured now. It helps to separate three moments: when a camera made an image, when a service stored or distributed it, and when your browser asked for it. The word “live” often folds those into one reassuring label. For a still image, that is too much certainty in too little space.

TfL describes its JamCam material as traffic-camera data and documents the service through its open-data guidance. That tells you who supplies the material and how the feed is offered; it does not turn every image into a continuously verified window onto this second. A refreshed page is an event in your browser. It is not, by itself, a certificate of the camera’s capture time. See TfL’s open-data guidance for its description of camera publishing.

A stored copy adds another step. Web systems can keep a response so it can be reused instead of fetched again. The rules and timing depend on the response and the route between services. A file name, a moving page spinner or a new browser request cannot reveal the moment a scene was photographed unless the image itself carries reliable time information and someone has verified what that marking means.

What “live” is useful for

For casual viewing, a camera can still be useful when its exact age is unknown. It can show how a junction is arranged, which buildings frame a street or how one approach meets a bridge. Those are observations about the displayed frame. They do not require a claim that the scene is current to the minute.

Movement changes the question. A clip gives you a sequence to watch, but playback only proves that the browser can play the supplied media. It does not establish continuous coverage between frames or tell you when the footage was recorded. Video container and codec are separate technical details: the container is the wrapper, while the codec describes how the picture was encoded. A playable file can still be old. The MDN guide to media containers explains that file type alone is not a timestamp.

When a decision depends on conditions now, such as a journey, disruption or road closure, use the relevant current official information. A camera frame may add context, but it cannot confirm a condition beyond its crop and its unknown capture time.

Choose the right evidence

Start by writing the claim you hope to make. “The bridge approaches this square from the south” is a fixed layout question; a map and a camera view can help you orient yourself. “Traffic is clear right now” is a changing condition; it needs current, time-stamped evidence. “This clip shows a bus turning” is a statement about visible motion, not a statement about today.

Look for a date or time printed inside the original image, then ask who placed it there and whether it marks capture, publication or another system event. Provider labels and page text can be useful clues, but they are not independent verification. The TfL API portal documents an interface for data access; an API response timestamp, where present, should not be silently renamed as the camera’s capture time.

For two images, compare their fixed shapes first. If their capture times are not verified as shared, a difference in vehicles cannot show which street is busier at one common moment. Keep the observation narrow and you keep the useful part.

A Westminster test

Open the Westminster Bridge and Parliament Square views as two different compositions. In the first, choose a durable line such as the parapet or road edge. In the second, identify an edge of the square or a building line. Those features help distinguish the places even if the traffic, weather or image age is uncertain.

Now ask a time-sensitive question: “Is the approach clear for my journey?” The frames cannot settle it. Their positions show only a bounded view, and a still cannot say what lies beyond the image. Treat the camera as orientation, then consult TfL’s current journey and status information before acting. A camera is a window with a frame; its limits are part of what it tells you.

One careful habit makes these pages more useful: state what you can see, name what would need a timestamp, and leave the second claim unanswered until you have the right evidence.

Sources & further reading

Official references inform this guide. Check the responsible organisation for current access, opening times and travel advice.