Why not just draw a black box in any editor? Some editors keep the original underneath, or let the box be moved off later.
Redact paints the covers into a brand-new picture, checks it pixel by pixel under every cover, reads it again for anything missed, and strips location and phone details before Save appears.
Android app with no internet permission, not on Google Play: https://redact.anonacondacodelab.com/android.html