How do I minimalise distortion on fluid images, and how do I also add a Gaussian Blur to that image?

Question

i have a website where I have 2 users

Problem a. User A doesn't add a banner image. So we have to enlarger their profile image. When enlarging it I am getting distorted.

Problem b. How do I add a Gaussian blur

Problem c. How do I then make that image fluid

Codeigniter PHP

Hope you can help