While there has been a long line of British naval vessels to bear the name Defiance, including a torpedo school ship and three United States naval vessels, there never was an HMS Defiant serving in the Royal Navy in real life. A fictional Defiant was seen in the 1962 movie Damn The Defiant! (based on the Frank Tilsey novel Mutiny), which may have been the namesake for the Constitution-class starship.
The painting depicted a ship-of-the-line warship. Dependent on the number of guns, a ship-of-the-line was ranked from first-rate (greatest number of guns) to fourth-rate (lowest number of guns). Based on the number of gun decks visible, three in total, in the painting, the Defiant was either a first-rate or a second-rate ship. The difference between a first-rate and a second-rate could be as few as two guns (though firing lighter shot) and, without knowing more about the Defiant, it's not possible to conclusively decide the ship's rating. The six real ships named HMS Defiance that served during the 18th century were all third-rate or smaller.