Back in the 70’s and 80’s, Larry Sultan and Mike Mandel were altering billboards with obscure images for the purpose of documenting their work with photos.  Often having no meaning at all, they were simply mocking advertising in general.  Their work is often overlooked when crediting pioneers of “street art”, while their efforts were long before there was a label.  Larry Sultan and Mike Mandel also produced a book titled “Evidence”, which is arguably on of the most influential books on the subject of using found images.