I'm having some serious troubles with my android camera application.
Either it directly tells me that it's not working ("Camera failed" in WhatsApp), or it allows me to take a picture - but that picture is just a full gray image with some stains on it (looks a little like this https://static.vecteezy.com/system/resources/previews/000/119/257/large_2x/gray-paper-texture-background-vector.jpg for instance). However, through the "viewfinder" everything looks perfect - so the camera hardware itself should be fine.
My guess: The SD card is damaged. I can't download any pictures from my web browser or send / receive images via WhatsApp (or any other app). But, I CAN access the files on the SD card, so there is also some evidence against a corrupted SD card.
Details: Phone: Lenovo K6 OS: Android 6.0