A simple class to perform image blurring by overriding the main RenderTexture.

Blur.cs

using UnityEngine;
using UnityEditor;
using System;
using System.IO;
using System.Linq;
using System.Collections;
using System.Collections.Generic;
using System.Text.RegularExpressions;

public class Blur {

  Color tint = Color.black;
  float tinting = 0.4f;
  float blurSize = 4.0f;
  int passes = 8;

  Material blurMaterial;
  RenderTexture destTexture;

  public Blur(int width, int height) {
    blurMaterial = new Material(Shader.Find("Hidden/Blur"));
    blurMaterial.SetColor("_Tint", tint);
    blurMaterial.SetFloat("_Tinting", tinting);
    blurMaterial.SetFloat("_BlurSize", blurSize);

    destTexture = new RenderTexture(width, height, 0);
    destTexture.Create();
  }

  public Texture BlurTexture(Texture sourceTexture) {
    RenderTexture active = RenderTexture.active; // Save original RenderTexture so we can restore when we're done.

    try {
      RenderTexture tempA = RenderTexture.GetTemporary(sourceTexture.width, sourceTexture.height);
      RenderTexture tempB = RenderTexture.GetTemporary(sourceTexture.width, sourceTexture.height);

      for (int i = 0; i < passes; i++) {
        if (i == 0) {
          Graphics.Blit(sourceTexture, tempA, blurMaterial, 0);
        } else {
          Graphics.Blit(tempB, tempA, blurMaterial, 0);
        }
        Graphics.Blit(tempA, tempB, blurMaterial, 1);
      }

      Graphics.Blit(tempB, destTexture, blurMaterial, 2);

      RenderTexture.ReleaseTemporary(tempA);
      RenderTexture.ReleaseTemporary(tempB);
    } catch (Exception e) {
      Debug.LogException(e);
    } finally {
      RenderTexture.active = active; // Restore
    }

    return destTexture;
  }
}