It’s a tough call from the OUTSIDE, but an X-ray clearly shows a bone spur in sharp contrast, like other bones and a tophus as “fuzziness.”
Location plays a part as well, for example a lump sticking out the back of a heel is usually a spur. A non-pointy lump at the bunion joint is usually a tophus. A POINTY lump is usually a BUNION.
Fingers are especially tough becasue tophi and the nodes of osteoarthrits look pretty similar.
X-rays are misread every day and I’m sure some hands were even misdiagnosed as FEET.
And history can help. For example, If you’ve had 3 gout attacks and you see a new lump, odds are VERY good it’s gout.