An estimate made from a picture has nothing to work with except the picture. Four things decide how close it lands.
Light
Daylight or a well-lit room. A dark frame hides the texture that says what the object is made of, and material is half the answer.
Background
A plain table, a sheet of paper, the floor. A patterned surface makes the object harder to separate from what sits behind it.
Angle
Shoot the whole object at a slight tilt rather than straight down. A top-down photo flattens it, and volume carries a lot of the result — from directly above, a tall jar and a flat lid look much the same.
A size reference
Worth trying, though not a guarantee. Lay a coin, a battery or a ruler flat beside the object and there is a known size to work against. Coins are easiest to find, and one denomination is always the same size.
It does not always help. In our own testing a reference improved some results and made others worse — a mug we had weighed at 264 grams came back as 10 once a battery was in the frame. Shoot it both ways when you can. The guide on how accurate this is covers what we measured.