Dheera Venkatraman has published an article describing how to attack blurring image to conceal information.
In the article, he describes :
Undoubtedly you have all seen photographs of people on TV and online who have been blurred to hide faces.
For the most part this is all fine with peoples’ faces as there isn’t a convenient way to reverse the blur back into a photo so detailed that you can recognise the photo. So that’s good if that is what you intended. However, many people also resort to blurring sensitive numbers and text. I’ll illustrate why that is a BAD idea.
And he gives suggestion to conceal information in images, we should just color over them.