I'm the developer behind Redact.Photo [0], instead of blurring or pixelating the image, I've added an additional step to improve data security. See "how it works" section on the page.
1. Image is scaled down to create a mosaic effect
2. Pixels are moved around a random offset of x and y axis
3. Blurring is applied
Adding black bars over information will always be better but this does result in more smooth redaction that I think cannot be undone because of the randomisation step.