This image was acquired from
wikimedia. It was marked as Public Domain or CC0 and is free to use. To verify, go to the source and check the information there.
Keywords from Image Description:
Cmbr.svg jansky per steradian where jansky is Watts per squaremeter per Hertz The horizontal axis corresponds to the reciprocal of the microwave wavelength in cm which is proportional to the microwave frequency The error bars are too small to be displayed by computer screen but were included to demonstrate the impressive accuracy