Can you win material by attacking a cannon's screen?
These answers restate the rules implemented by our open-source engine, which follows the WXF laws and is regression-tested against the official 110-diagram repetition casebook. Where an answer refers to a specific position, that position lives on the linked reference page, where the build verifies it against the engine before publishing.
Direct answer
Sometimes, yes, and it is a doubly useful capture when it works. If a cannon's screen is an undefended piece, capturing it wins material in the ordinary way, but it also does something extra: it removes the screen, switching off whatever the cannon was threatening through it, all in a single move.
Two gains from one capture
Most captures either win material or improve your position; this kind does both at once. Before capturing any piece that happens to sit between an enemy cannon and something valuable, check whether taking it also defuses a threat you would otherwise have had to answer separately.
When it does not work
If the screen is well defended, capturing it simply loses the exchange, and the cannon's threat is switched off at your expense rather than theirs. The idea only pays off when the screen itself is loose, check its defenders before committing to the capture, the same as you would for any other piece.
Related questions
Is this the same as removing a screen defensively?
Related, but distinct, this is about winning material from the screen itself, not just defending against the cannon's threat by moving a screen you control.
Can this work against your own cannon by accident?
Yes, an opponent capturing your own screen can switch off a threat of yours the same way, which is worth watching for when a piece you are relying on looks undefended.
.