1. An apparatus for overlaying a plurality of images, comprising: a broadcast receiver configured to receive broadcast signals and output a video signal based on the broadcast signals, wherein the broadcast signals are at least one of digital multimedia broadcast signals and digital broadcast signals; a broadcast image layer generator configured to generate a broadcast image layer based on the output video signal; an application image layer generator configured to generate an application image layer based on an application image of an application while a broadcast image is being displayed, wherein, for each pixel in the application image, if the each pixel represents at least a portion of text, the application image layer generator adds a desired mark value representing a text pixel to the color information of the each pixel, and, if the each pixel does not represent text, the application image layer generator adds a desired Alpha value representing a degree of translucency to the color information of the pixel; and an overlay processor configured to generate an overlay image obtained by overlaying the broadcast image layer with the application image layer, the overlay image being based on the color information of the broadcast image layer and the application image layer and the overlay image including a simultaneous display of the broadcast image corresponding to the broadcast image layer and the application image corresponding to the application image layer, wherein, when the application image includes the text pixel with the mark value in the color information, the overlay processor applies a color to the text pixel based on a color of a background to identify the text pixel against the background.