There are two solutions to this. First, when using a jig, take the sock and slightly roll it so the imaged area moves to the other side of the jig. The more careful you are with this, the less likely you will have a noticeable line.
The second solution is to get socks that have a black interior so you don’t need a jig. The black will show through slightly when the customer puts them on their foot, but you’ll have a good-looking sock without the hassle of a jig.
-Aaron Montgomery, 2 Regular Guys, MontCo Consulting