I sell stock photography as a small side gig and the company is based out of AUS. They collect Withholding Tax, I am just unsure of how to document this for the IRS.

[surgerygalore]

hello

if you are a US citizen, you will have to pay US income tax on the income you generate worldwide - this holds also if you are not a US resident, only citizen

When you declare your income in AUS to IRS, and depending on the USA-AUS tax treaty if any, typically you may consider foreign taxes paid as a tax credit

a bit delicate, in particular if there are tax treaties in effect - a "trick" would be to have a professional specializing in this type of situation do your first return - you will then be able to mimic the future ones!