Just rotate the camera to 90 degrees along the z axis(the camera is which is rendering the webcamtexture gameobject).

I found next solution.

1) Create new shader:

 Shader "Custome/Web Camera Shader" 
 {
      Properties 
      {
          _MainTex ( "Main Texture", 2D ) = "white" {}
     }
     
     SubShader 
     {
         Pass
         {
             CGPROGRAM
             
             #pragma vertex vert
             #pragma fragment frag
             
             uniform sampler2D _MainTex;
             uniform float4x4 _Rotation;
             
             struct vertexInput
             {
                 float4 vertex : POSITION;
                 float4 texcoord : TEXCOORD0;
             };
             
             struct vertexOutput
             {
                 float4 pos : SV_POSITION;
                 half2 uv : TEXCOORD0;
             };
             
             
             vertexOutput vert(vertexInput v)
             {
                 vertexOutput o;
                 
                 float4 newPosition = mul( UNITY_MATRIX_MVP, mul(_Rotation, v.vertex) );
                 
                 o.pos = newPosition;
                 o.uv = v.texcoord;
                 
                 return o;
             }
             
             float4 frag(vertexOutput i) : COLOR
             {
                 return tex2D( _MainTex, i.uv );
             }
             
             ENDCG
         }
     }
     Fallback "Diffuse"
 } 

2) Apply shader to material of a plane you want to display WebCamTexture

3) Set matrix for the material (in Start() method):

 Quaternion rotation = Quaternion.Euler (0, 90, 0);
 Matrix4x4 rotationMatrix = Matrix4x4.TRS (Vector3.zero, rotation, new Vector3(1, 1, 1));
 gameObject.renderer.material.SetMatrix ("_Rotation", rotationMatrix);

4) Set WebCamTexture to material texture like this (in Update() method):

 cameraScreen.renderer.material.mainTexture = webCamera.texture;

Great ideas here!

I am new to Unity IOS. I have tried to do the matrix bit to the best of my abilities with no luck. Iamdain could you please explain your solution in more detail? From a newbies point of view maybe?

Hi Iamdain, I'm having the same problem but am stuck in trying to create the correct inputs for the TRS function. What scale did you use to get the proper flip of the rawdata from the iOS device? Thanks in advance for your help! -Amy

Guys the solution I used was to apply a transform matrix which is processed in the shader.

Just use what you need from here:

http://docs.unity3d.com/Documentation/ScriptReference/Material.SetMatrix.html

You can just add "matrix [_Rotation]" to your shader pass in your existing shader if you don't want to build your own shader at run-time as they did in this example.

The full transformation matrix is built for you so you don't need to understand how the 4x4 Matrix works internally, just plug in your offset, scale and rotation values. http://docs.unity3d.com/Documentation/ScriptReference/Matrix4x4.TRS.html?from=Material

The real problem I have at the moment is HOW DO YOU DETECT THE RESOLUTION OF THE CAMERA???? You can't scale the resulting image to give the correct aspect ratio without knowing this making the feature fairly useless. Is there something I missed here? I need to build for iOS and Android, have only just hit this problem so will post back if I find a solution.