i say its about 3.5-4lbs.
i dont accuse you of lying, or trying to exaggerate, im just saying my opinion, everythings cool.
if you say your knuckles are 4.5" across, judging by that, the fish is about 19, maybe 20 inches long, and according to the weight calculator on Bass Resource (which almost everyone agrees weights fish too high), that fish would weigh 3.9lbs (19 inches) or 4.5lbs (20 inches).
there is really no way to tell from a photograph, especially when accurate lenght and girth measurements are not given. but i can tell that is no 5lber.
if you do have the length and girth but didnt post them, try using this formula to find out the weight: (girth2 × length) ÷ 800
most people will tell you this is a pretty accurate formula.
might i add, NICE FISH!!! its still bigger than most of what i catch, good job!