You are technically correct assuming your dividends aren't of the qualified variety. In that instance you don't pay capital gains, you instead pay full-fat income taxes!

Capital gains are, however, absolutely owed on qualified dividends.

In either case (with the added assumption that we're talking about securities held in a non-tax-advantaged account), your brokerage will send you an IRS form 1099-div.

https://www.investopedia.com/ask/answers/011215/if-i-reinves...