DOOH ad verification, explained
Proof of Play vs Proof of Display
Two things the industry calls proof. One is the playback system’s account of its own work; the other is an independent observation of the screen. This is what each can and cannot claim.
The short answer
What proof of play actually proves
Proof of play is the playback log generated by the media player software itself. When a player runs a scheduled item, it can record that it issued the play command, decoded the file, and rendered frames inside its own pipeline — then report that record back to the CMS as evidence the content played. Almost every DOOH player produces some version of this log. For day-to-day fleet operations it is useful: scheduling reports, play counts, delivery pacing.
This is not a flaw that better software could fix. Proof of play is self-attested. The player is grading its own work. It can tell you what it believes it did, but nothing in that log requires the output to have reached a lit, correctly wired screen. A play event and a play are not the same claim.
A playback log built this way cannot, on its own, distinguish a genuine play from:
- A screen that's switched off or lost power downstream of the player
- No signal reaching the display, from a loose or failed HDMI connection
- The screen showing the wrong input source
- The panel physically obstructed — by a poster, a crate, or a closed shutter
- The player rendering a frame internally without it ever leaving the device
What Proof of Display proves
Proof of Display starts outside the player. An independent sensor — Vojo's Harvester — watches the screen itself. It doesn't ask the player what it thinks happened; it observes the display and captures a fingerprint of whatever content is genuinely on the glass. Because the sensor is a separate physical device, a fault in the player can't also take down the thing verifying it.
That fingerprint is matched against the scheduled campaign. A verified play means something specific: this exact creative was confirmed present on this exact screen, at this time, by a system with no stake in the player's own report. If nothing usable was captured, that's recorded too — and it's just as valuable.
- Confirms the screen was powered on and displaying an image
- Confirms the correct content was showing, not a fallback or wrong input
- Catches black screens, freezes and stuck frames the player never reported
- Detects obstruction — nothing usable to fingerprint means nothing was seen
The test
What independent has to mean
Independence has two halves, and they get conflated. One is who reports — is this the seller's own account, or a third party's? The other is where they stand — inside the system being checked, or outside it? A playback log fails both. In-creative measurement passes the first and not the second. Only a sensor on the panel passes both.
The question to ask
Would this evidence still exist if the delivery system were lying, broken, or simply switched off?
Only one method answers yes
A sensor watching the panel does not need the player, the CMS, the network, or Vojo to be telling the truth. In-creative measurement is still third party and still not the seller's account, but it lives inside the render, so it cannot answer this one.
That includes us. Proof of Display does not require Vojo to have delivered the ad, and it works on screens running someone else's CMS and someone else's player. If our proof needed our delivery, it would be one more party vouching for itself.
Side by side
What each method can claim
| Capability | Proof of play | In-creative | Proof of Display |
|---|---|---|---|
| Source of evidence | The player's own local log, the device reporting on itself | Measurement code inside the creative, reporting from the player's render | An independent sensor watching the screen from outside the player |
| What it detects | That content was dispatched and a play event was recorded | That the creative was loaded and rendered in the player's environment | What actually appeared on the glass, matched to the campaign by fingerprint |
| Independence | Self-attested: the same system that failed is the one reporting the failure | Independent of the operator's log, but still runs inside the player stack | Independent of the player, so it still catches faults the player can't see |
| Catches a black or frozen screen | |||
| Catches wrong input or no signal | |||
| Catches physical obstruction | |||
| Dispute value with an advertiser | Circumstantial: it's the seller's own record, offered on trust | Stronger than the seller's own log, yet still blind to the physical screen | Evidentiary: a third-party measurement neither side had to take on faith |
Choosing
Which one do you actually need?
Not every screen needs independent verification, and pretending otherwise is how verification gets sold to people who will not get their money back. The question is what a delivery argument costs you.
Playback logs are enough
Your own content, internal comms, or advertising sold on relationships where nobody has ever asked you to prove a spot. The log answers the questions you actually get asked, and it is already free.
In-creative measurement earns its place
You are the buyer, running one campaign across networks you do not own. You cannot fit hardware to somebody else's estate, and you need the same measurement everywhere the creative goes.
Independent Proof of Display pays for itself
Premium sites, audited buyers, or a rate you are trying to defend. Anywhere you are already over-delivering to cover a number you cannot prove — that cushion costs more, every flight, than the sensor does once.
These are not exclusive, and most estates end up mixed: logs everywhere, sensors on the sites where the proof changes the price. Fitting every screen is rarely the right first move.
Where Passport fits
Creative wrappers (Vojo Passport) give advertisers content-level verification from inside the render — independent of each operator's log, on any network the creative runs on. That is not Proof of Display. Passport sits on the same side of the glass as the player; PoD is produced by a sensor watching the glass from outside.
On Harvester-equipped screens the two work together. Elsewhere, Passport still gives the buy side a consistent campaign record without overclaiming glass-level proof. Read about Vojo Passport.
Frequently asked questions
What is proof of play in DOOH?
Proof of play is a playback log generated by the media player itself: a timestamped record that says content was dispatched and, according to the player's own software, played. It's useful operational telemetry, but it is self-attested — it describes what the player believes happened, not what independently happened on the screen.
What is Proof of Display?
Proof of Display is independent, sensor-based verification of what actually appeared on a screen. A separate device (Vojo's Harvester) observes the display itself, fingerprints the content it sees, and matches that fingerprint to the scheduled campaign. It answers a different question: not "did the player try to show this" but "did this actually appear on the glass."
Is proof of play the same as Proof of Display?
No. Proof of play measures the player's intent and internal state; Proof of Display measures the outcome on the screen, independently of the player. A player can log a successful play while the screen is black, showing no signal, or physically obstructed — and proof of play won't catch any of those. Proof of Display will, because it never asks the player to grade its own work.
Why can't proof of play detect a black screen or no signal?
Because most proof-of-play systems log at the software layer: the player confirms it issued a play command, decoded a file, or rendered a frame in its own pipeline. None of that requires the output to have reached a lit, correctly-connected display.
What about creative wrappers and in-creative verification?
A creative wrapper is measurement code that ships inside the creative and reports from within the player's render. It gives the buy side an independent record of the render, but it measures from the same side of the glass as the player — so it complements Proof of Display rather than replacing it. Vojo offers this as Vojo Passport (content-level verification, never called Proof of Display).
Is Proof of Display patented?
Vojo's Proof of Display method is patented, with granted patents in the United Kingdom and the United States, and a European patent application pending.
See Proof of Display in practice
Vojo's Proof-of-Display technology is protected by granted patents in the United Kingdom (GB2583366, GB2597434) and the United States (US 12,176,999), with a European patent application pending.