Your screenshot appears to be "clean" - without any evidence of unexpected screen artefacts or defects. If screen artefacts are visible when looking at the screen (and can be "captured" when photographed by another device), but are not visible in a screenshot, then you have a screen hardware problem.
Some conventional edge-lit LCD screens can exhibit small bright patches throughout the visible screen area, these being visible to the naked eye when the screen is uniformly white. Where seen, these patches are characteristic of partial delamination of the backlight diffuser layer. This type of screen defect, if present, can only be rectified by replacing the entire screen assembly - the screen being the single most expensive component of the iPad.
For avoidance of doubt, backlight diffuser delamination is distinct from another type of screen defect - where bright patches are seen around the periphery of the screen. Bright or dark patches seen around the edges of the screen are usually attributable to partial failure of the edge backlights themselves - as opposed to the diffuser layer that evenly distributes the light across the entire screen.
Visible screen issues that are not captured by a screenshot (and are not visible when the screenshot image is viewed on a different screen) likely indicate a hardware fault that requires repair. By contrast, image artefacts that are captured by a screenshot are usually due to software - and are not a hardware fault.
You might be best advised to visit the Genius Bar at your local Apple Store or Apple Authorised Service Provider (AASP) - where you will be able to demonstrate the issue to an Apple Technician. Your iPad can be tested and assessed; if a fault is identified, you'll be in the possible place to explore your available options:
Genius Bar Reservation and Apple Support Options - Apple