The portrait shows Duff wearing a floor-length, white gown. A simple headband with pearls keeps her blonde hair off of her face.
She is holding a bouquet of pink roses as she smiles next to her new husband, who is wearing a dark blue tuxedo, white shirt and black bow-tie.
The newlyweds are standing in front of a station wagon with wood panels and the message, "Just Married," is written on the back window. Tin cans are tied to the bumper.
Duff also shared a video documenting for Vogue magazine why she chose this particular frock for her big day.
"Really enjoyed filming this with @voguemagazine so fun to talk about my beautiful dress and how it came to be!" Duff captioned the clip.
She described the Jenny Packham ensemble as comfortable and modern with clean lines and structure.
Vogue reported Duff and Koma -- both 32 -- tied the knot at their Los Angeles home over the weekend.
Duff was previously married to hockey player Mike Comrie from 2010 to 2016. They have a 7-year-old son.