Try Quick Mask to blur part of picture you want.
You can apply pixelate or blur effect quickly and easily.

Features
∙ Pen and rectangle tool to select area
∙ Various effect such as blur, pixelate, etc. (Some effects are not supported in iOS 8)
∙ Change strength of effect
∙ Undo/Redo
∙ Sharing to other apps
∙ Edit picture directly in Photos app (App Extension)
∙ Video Mosaic, Trimming, Cropping
∙ Emoji attachment function
∙ Image cropping function
∙ Face and text recognition