How to uncover blacked out text? Is it even possible?

PNG is a bitmap format, thus "blackening out" is a destructive method: what was in the original picture before it was replaced by black pixels is no more in the blackened picture. You can use any fully opaque color (a color without a transparent value) for this process, not just black. This is not the same for other formats that are layered, like PDF, SVG (vector image), PSD (photoshop image), etc. In those formats, "blackening out" will most likely add a black layer that can easily be removed later. PNG doesn't have EXIF metadata like JPEG, but still can embed some king of metadata in the ancillary chunks. You would be wise to check what's contained in those chunks of your picture.

How To Uncover Blacked Out Text For a screenshot, if you used the exact same shade of black for both you are just out of luck. Simply put, both text and pictures are coded the same way for image files, and so if they are set to the same shade, the computer has no way of telling them apart. If they are very slightly different shades, try messing with contrast or setting to black and white then adjusting the choice point for black/white until it pops out.