Unity shows me a picture of a screen whenever I mouse over the game screen.

Titlescreen = Splashscreen? $$anonymous$$y guess is, you did something wrong in you code. So it is difficult to tell you much of anything out of the blue.

Have you tried looking where that picture is referenced in your project. And check where that variable holding the image is all being used for. (Should obviously be in your OnGUIs)

the image is never referenced in the scripts. The image is a screen shot of my game. I took the screenshot, imported it into my assets, and pasted it on to a plane with an OnGUI script attached to it. The script has stayed the same but now even when the OnGUI isn't there it still shows up. Is there like a setting that I might have accidentally changed?

ok.. If you put that image on a plane (in a material), you don't need OnGUI() to display it. OnGUI is only for 2D. So I guess something must be doing something with that plane of yours. Have you checked where that is referenced in your scripts?

I only use OnGui to display the title and the buttons. And the plane is only referenced in that 1 OnGUI script. It's only started to act up now, but the OnGui was working fine earlier.

Add a splashscreen (Your Intro image) in Build settings->player settings->splash image. If you wish to make a separate Title screen you should include it as a New Scene and detect a Touch Event on it to begin a call of :

 Application.LoadLevel ("First Level");

The reason it shows up when you touch anywhere is because mouse events and touch events are handled differently. If you do not use a proper Touch Handler a touch to the screen is the same as touching everything in view.

A touch handler looks something like the following and in this case it uses a raycast (shoots a line) from the screen touch position directly into the world and tests to see what the ray touches. Here, "StartGame" is the name of a 3DText object, but for you, you can set your image as a GUITexture for much the same effect. Note that my 3DText object has a Box Collider on it so I can detect the hit of the ray. GUITextures don't require a collider and live in the Camera space rather than the 3DWorld space.

 function Update ()
 {
     if (Input.touchCount > 0) 
     { 
         // If there are touches... 
         var theTouch : Touch = Input.GetTouch (0); 
         // Cache Touch (0) 
         var ray = Camera.main.ScreenPointToRay(theTouch.position); 
         
         
         if(Physics.Raycast(ray,hit,500)) 
         {
             colName = hit.collider.gameObject.name;
             if(Input.touchCount == 1) 
             { 
                 if (theTouch.phase == TouchPhase.Began || theTouch.phase == TouchPhase.$$anonymous$$oved) 
                 { 
                     if(hit.collider.gameObject.name == "StartGame")
                     {
                         Application.LoadLevel ("TC1");
                     }
                 } 
                 //if (theTouch.phase == TouchPhase.$$anonymous$$oved) 
             }
         }
     }
 }

If this doesn't make sense, check out the Penelope iPhone tutorials and check out the Android build of the AngryBots tutorial. The Joystick prefab in the latter contains the Touch Handler and is worth a look.

Edit: OnGUI() is very expensive for most uses. $$anonymous$$ost people (and the stats/profiler) recommend you avoid it like the plague.