Blurry or broken camera
Before suspecting the hardware, a simple restart or force-closing the app solves a good share of camera problems - the rest comes from a physical module knocked out of alignment or dirty after a drop.
FAQ by brand
Apple (iPhone)
“Cannot activate camera” - what should I check before a repair?
This message can come from a third-party app blocking camera access or, after a drop, from a camera module that has come loose from its connector. A restart rules out the first cause before moving to a hardware diagnosis.
The lens is clean but photos are still blurry - why?
It can point to an autofocus or optical stabilisation (OIS) problem after a knock, which needs the camera module replaced rather than just cleaned.
Samsung
The same spot appears on all my photos, even after cleaning the lens?
That's dust that has got inside the module, between the lenses - invisible and impossible to clean from outside. A technician has to open the module.
The camera closes on its own (crashes) when I open it?
Start by clearing the camera app's cache and checking for system updates - most crashes of this kind are software, not hardware.
Xiaomi, Huawei
Night or portrait mode disappeared or stopped working after an update?
That's usually down to the software update (MIUI/EMUI) rather than the sensor itself. Check the release notes or reset the camera app's settings before considering a hardware diagnosis.
Other brands
How can I tell whether it's software or hardware?
Test the built-in camera app after a restart, and try a third-party camera app if you can. If the problem shows up everywhere and survives a restart, that's a good sign a hardware diagnosis is needed.
Your problem isn't listed here?
Every device is different - ask for a free diagnosis or describe the problem directly on WhatsApp.