I'm using the stock Samsung S8 Photo editor and it lets you do that. In the past I've used Snapseed but that doesn't really offer a blur option, you just have to manually play with the settings to get that distorted effect, but I'm guessing maybe Photoshop Express might?
As for the app locker, the one I've used is Samsung's Secure Folder or My Knox, just not sure if the latter works in non-Samsung phones or not.