how to play a slideshow of images?

i want to show 3/4 jpegs to create a slideshow. I have the following code:

`using UnityEngine;
using System.Collections;

public class SlideShow : MonoBehaviour
{
public Texture2D[] slides = new Texture2D[9];
public float changeTime = 10.0f;
private int currentSlide = 0;
private float timeSinceLast = 1.0f;

void Start()
{
guiTexture.texture = slides[currentSlide];
guiTexture.pixelInset = new Rect(-slides[currentSlide].width/20, -slides[currentSlide].height/20, slides[currentSlide].width, slides[currentSlide].height);
currentSlide++;
}

void Update()
{
if(timeSinceLast > changeTime && currentSlide < slides.Length)
{
guiTexture.texture = slides[currentSlide];
guiTexture.pixelInset = new Rect(-slides[currentSlide].width/20, -slides[currentSlide].height/20, slides[currentSlide].width, slides[currentSlide].height);
timeSinceLast = 0.0f;
currentSlide++;
}
timeSinceLast += Time.deltaTime;
}
}`

but pictures are offset and not to scale. any help please?