How to stretch an image i have in Unity into a ratio that matches the image target - Using Cloud Reco

Hi guys, I need an Image to completely overlay the marker image i see through the camera feed. For this i might need to know what amount of pixels the marker occupies over the screen , So I could  stretch the image i have inside the unity so the image could completely overlay the target image. I have no idea how to achieve this. Also i am using cloud target to achieve this , Kindly help me know how i could successfully do the stretching. Kindly look into to the attachment too which could provide you with further idea of what i am intending to do.

Thanks.