The most common case you should notice is the classical oil painting, where brush strokes are meant to be placed with various styles, yet to produced an overall contrast and brightness that resemble the scene when the piece is viewed from some distance away (I figure there are still many who got very curious why painters just love to stop in the middle and step away from their work to exam their paintings). However, if you have a close up of an oil painting, the strokes probably can be mean nothing in terms of shape or shade, unlike the traditional asian or Mediterranean paintings. In this way, low spatial frequency dominates the information of the image, while the high spatial frequency demonstrates the styles of the painters (specially for the impressionists, such as Van Gogh ).
To even further demonstrate the concept, I have a new drawing that I did using photoshop and digital tablet. You can try to compare the photograph taken, and the drawing to see the effect of spatial frequency.
1. Get two black and white face images with their face aligned (better to use images with dark backgrounds);
2. Blur one of the image with Gaussian filter with radius of your choice (this depends on how far you want to see the hidden image from far away).
3. Set the combine mode to screening and adjust the top layer's visibility to roughly 90%
4. Combine layers.
Now you should have something very similar.