Because it is self-employment income. You earned it by creating and working for yourself.
The system will create a schedule C for you. You will be able to deduct any expenses for art supplies and equipment needed in order to create the pieces and earn that $1000. The system will also suggest other expenses related to being an artist that might be deductible. In the end if you have any profit left after deducting expenses that profit is taxable. If you have a negative number then it will reduce your other taxable income.
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