I altered one of my 'housey' pictures a few weeks ago. It hadn't been sold at the exhibitions it went to and I didn't put it up for sale on my website because the frame had got slightly damaged & it also had glass [nervous about sending large pictures with glass through the post - I smashed one with glass just putting the picture in it!].
Anyway I took it out of the frame and wrapped it around a canvas frame and then painted over the whole thing with acrylic paints. I then applied metallic oil pastels and went over the stitching with black. The picture looks different colours from different angles. I prefer it to the original, which is shown below the collage.