Sepia Photoshop Images Effect

1. Open an image that you would like to manipulate. Make sure your image is in RGB mode. To check this, go to Image under the menu bar - Mode - RGB Color.
Make a duplicate of this layer as you will be working on this layer going forward.

2. Images - Adjustments - Desaturate

3. Images - Adjustments - Channel Mixer and use the following illustrated values.

and you are done. cheers !