Is this as good as a real scanner?
For paperwork, close enough that the difference stops mattering: even lighting, level text, and a few hundred kilobytes instead of several megabytes. A flatbed still wins on anything you have to reproduce exactly — art, photographs, pages where the paper's own texture is the content.
Do my photos get uploaded?
No. The correction and the PDF are both built in this tab, by this device. That is the reason to use this rather than a scanner app: the documents people photograph are passports, payslips, contracts and bank letters, and those are exactly the files you do not want sitting on somebody else's server.
Why do scanner apps leave a black corner, and does this?
It should not, and avoiding it is the specific reason this tool exists. A simple filter picks one brightness cut for the whole image, so a corner in shadow falls below the cut and turns solid black. Here the lighting is measured across the page and divided out before anything is decided, so the shadowed corner and the sunlit edge end up the same white.
Black and white, greyscale or colour?
Black and white for ordinary paperwork — smallest file, most readable. Greyscale when the page carries photographs or shading worth keeping. Colour when the ink's colour is part of the meaning: a signature, a stamp, a highlighted clause. Every mode corrects the lighting; only the last keeps the hue.
Can I use photos I already took?
Yes, and it is often the better route: take the pictures with your normal camera app in good light, then add them here. Anything the browser can decode works, including HEIC on iPhone and iPad, because the decoding is done by the device rather than by a library we ship.