If you have specified a set for a card in a deck, we will try to use the corresponding image when possible. However, we unfortunately don't have images for all printings available, so some sets may still display the incorrect image.
To specify the set when building a deck, put the set abbreviation in front of the card name. So for example instead of Cardname, you write [UNG] Cardname. In the text-based deckbuilder this is easily done. To do the same thing in the interactive deckbuilder, you need to use the manual card entry field for now. However, I am planning on adding a better solution for this in the near future!