An image display device mounted on a vehicle, the image display device comprising: a communication unit configured to receive encoded screen information of a mobile terminal and first control information of the screen information from the mobile terminal, the first control information includes an image size transformation information of the screen information and an image compression format information of the screen information; a controller configured to decode the encoded screen information based on the received first control information and to transform the screen information based on the first control information; and a display unit configured to output the transformed screen information to the original size, wherein the transformed screen information comprises a shared screen between the image display device and the mobile terminal, wherein the controller is further configured to: modify the image size transformation information and the image compression format information based on a status of a screen change, and control the communication unit to transmit second control information including the modified image size transformation information and the modified image compression format information, wherein the modified image size transformation information and the modified image compression format information are adjusted based on a performance status of the image display device or the mobile terminal, wherein the screen information is changed into a pixel format having a low color depth based on receiving a user input, and wherein the screen information is changed into a pixel format having a high color depth while displaying a still image. a communication unit configured to receive encoded screen information of a mobile terminal and first control information of the screen information from the mobile terminal, the first control information includes an image size transformation information of the screen information and an image compression format information of the screen information; a controller configured to decode the encoded screen information based on the received first control information and to transform the screen information based on the first control information; and a display unit configured to output the transformed screen information to the original size, wherein the transformed screen information comprises a shared screen between the image display device and the mobile terminal, wherein the controller is further configured to: modify the image size transformation information and the image compression format information based on a status of a screen change, and control the communication unit to transmit second control information including the modified image size transformation information and the modified image compression format information, wherein the modified image size transformation information and the modified image compression format information are adjusted based on a performance status of the image display device or the mobile terminal, wherein the screen information is changed into a pixel format having a low color depth based on receiving a user input, and wherein the screen information is changed into a pixel format having a high color depth while displaying a still image. modify the image size transformation information and the image compression format information based on a status of a screen change, and control the communication unit to transmit second control information including the modified image size transformation information and the modified image compression format information, wherein the modified image size transformation information and the modified image compression format information are adjusted based on a performance status of the image display device or the mobile terminal, wherein the screen information is changed into a pixel format having a low color depth based on receiving a user input, and wherein the screen information is changed into a pixel format having a high color depth while displaying a still image.