Why a plate is the worst thing to blur
Everything that makes a covering weak is true of a number plate at once. The string is short. The alphabet is small and known. The typeface is standardised and, in most countries, legally specified. The spacing is fixed. The ground is deliberately high-contrast, because a plate exists to be read at distance. And crucially, the set of plausible answers is finite and can be enumerated.
A recovery attempt against a plate does not have to reconstruct the picture. It only has to render every candidate string, apply the same covering, and see which one matches. That is arithmetic, not magic.
A solid fill defeats that entirely, because there is nothing left to compare against. This is the one place on the site where the recommendation is not a matter of taste.
What each covering leaves behind on a plate
| Covering | What survives | Worth using here |
|---|---|---|
| Blur | Stroke positions, character count, the light and dark rhythm of the string | No |
| Mosaic | One average per block, which on a seven-character plate is a handful of numbers per character | No |
| Solid fill | Nothing. The pixels are one flat colour and carry no information about what they replaced | Yes |
The longer version of this argument, with the same table extended across faces, signatures and account numbers, is in the covering-by-subject guide.
Selling a car, and the rest of the photograph
Listing photographs are where most of this happens, and they are usually taken outside the seller’s own house. Cover the plate, then look at the picture again for the things that came with it: a house number on a door or a bin, a street sign at the edge of the frame, a neighbour’s plate, a parking permit, a delivery label on a doorstep. Each of those is another drag, and together they are the difference between an advert for a car and an advert for where the car sleeps.
Questions about plates
- Why does this not find the plate for me?
- Because no plate detector has been downloaded, timed and licence-checked by this project. Every number on this site about a model's size or speed came off a file that was actually served, and the moment one of them is a guess the rest stop being worth anything. A plate is also the easiest thing on a photograph to find by eye and the fastest to cover: one drag along it and you are done.
- Is a mosaic enough for a plate?
- No, and a plate is the clearest case in the whole subject. A plate is a short string from a small alphabet, in a standardised typeface, at a standardised spacing, on a high-contrast ground. That is close to the ideal conditions for recovering characters from block averages: the number of possible strings is small enough to search, and each candidate can be rendered and compared against what the mosaic left.
- Does covering the plate make the car anonymous?
- No. A make, a model, a colour, a dent, a roof box, a parking permit in the windscreen and the house behind it all survive the plate being covered. If the point is that a specific car should not be identifiable in a specific place, the plate is the first region to draw and rarely the last.
- The plate is at an angle.
- Drag a rectangle that covers all of it including the corners that stick out, or switch to an ellipse and grow it past the ends. An angled plate is the case where people leave a character visible at one end, so it is worth checking the saved file rather than the preview.