first thing first getting a texture from the camera can be done with the help of Render texture in unity.

After getting the screen shot you can use EncodeToPng function to get the byte data... You can save it as it is into the disk or u can again convert it into string64 using this function. Either way you would have to use http://System.IO classes to save it to disk, I suggest using StreamWriter class... similarly u can use streamReader for retriving the image back...When you press delete you can delete the file previously created....!! Hope it helpy :)

For tumb nail of the texture in the GUI you can use Graphics.DrawTexture. For expanding the image you can use the same function.

This script lets you take screenshots and saves them next to your project, plus it draws a GUI texture of the last screenshot you took ;) Modify this for your own purpose. Add some animation and more GUI textures etc...

Put this on any object in your Hierarchy and drag any texture onto blankTexture. You can look at the "var url" in the inspector to see what file path is generated when you take a screenshot. This can be helpful for tweaking it...

private var count : int = 0;
var blankTexture : Texture;
var url = "";

function Update() {
    if(Input.GetKeyDown("s")) {
        ScreenshotEncode();

        }
}

function ScreenshotEncode() {

    yield WaitForEndOfFrame();

        var texture:Texture2D = new Texture2D (Screen.width, Screen.height, TextureFormat.RGB24, false);
        texture.ReadPixels(Rect(0.0, 0.0, Screen.width, Screen.height), 0.0, 0.0);
        texture.Apply();
    yield;

        var encoder:JPGEncoder = new JPGEncoder(texture, 100.0);

    while(!encoder.isDone)

        yield;

        File.WriteAllBytes(Application.dataPath + "Overwrite" + count + ".jpg", encoder.GetBytes());

        Grab();
}

function Grab () {

        url = ("file:" + Application.dataPath + "Overwrite" + count + ".jpg");

        var www : WWW = new WWW (url);
        yield www;
        //you can also put this script on a cube and it will render the texture
        //renderer.material.mainTexture = www.texture;
        blankTexture = www.texture;
        count = count+1;
       }

function OnGUI() {

        if(!blankTexture){
            Debug.LogError("Assign a Texture in the inspector.");
            return;
     }

        GUI.DrawTexture(Rect(10,200,360,260), blankTexture, ScaleMode.ScaleToFit, true, 1.0f);

}