Roger from what I gather in your original post you have a graphic image on the left side of the card that is to only cover the left 1/3 of the card then within 5mm blend to white, correct?
In photoshop using the wand tool with a tolerance setting of say 50, select the white side of the card. Then choose feather (option+cmnd+d) and feather the selection to about 24 pixels (assuming the original is at 300 dpi) then under filter choose Gaussian Blur and set it to about 20 and apply it to the selection. It may take 2 or 3 applications of the Blur to get what you want, but just keep hitting cmnd+f to repeat the blur filter until satisfied. Then select Add Noise and set it to about 1.7 and that will help make the blend a little smoother.
This will help to retain the integrity of the orange image without getting it to trashed.
Hope this helps