The degree of visibility of any kind of stimulus is largely determined by the background on which it is shown, a property commonly known as masking. Many psychophysical experiments have been carried out to date to understand masking of sinusoids or Gabor targets by similar maskers and by noise, and a variety of masking models have been proposed. However, these stimuli are artificial and quite simplistic compared to natural scene content. Masking models based on such experiments may not be accurate for more complex cases of masking. We investigate the visibility of noise itself as a target and use natural images as the masker. Our targets are Gaussian white noise and band-pass filtered noise of varying energy. We conducted psychophysical experiments to determine the detection threshold of these noise targets on many different types of image content and present the results here. Potential applications include image watermarking or quality assessment.