As to the form of submitting this information, copies of your own tax returns are acceptable, but the immigration officials know that it wouldn't take much for someone to forge these.
Therefore, they prefer to receive tax transcripts, which are generated by the IRS and show detailed information of your tax filings. The IRS offers a free online portal at which you can download and print your tax transcript immediately. Go to its "Get Transcript." page.
https://www.irs.gov/individuals/get-transcript
