I knew these had a familiar look. I owned one of a similar genre.
During the 1970s and 1980s, holographic metallic foil became the rage. It was used to make all kinds of art. In some cases, shapes were cut out of it to create silhouettes or mosaic pictures, or to add an accent to them. But there were three styles related to yours.
In one, the holographic foil was used as the background medium, and a picture was printed on it. Sometimes the foil was also etched with patterns that reinforced the picture detail. The foil gave the picture a somewhat 3D appearance; not quite holographic, but the picture popped off the background with a sense of depth, and you got the impression that from the right angle, you could see behind things in the picture.
One picture that was used for this, a number of times for some reason, was an apparently well known picture of Nell Gwynn's house (the version I owned):
A second way the foil was used was to etch some eye-catching graphic elements in it, and sometimes elements of the picture, and then print a picture on it that left the graphic portions of the foil visible. That gave a similar effect as what was previously described, but the foil, itself, became part of the picture. Here are a few examples:
Source & further information: Vintage Foil Art Picture Eagle Print Silver and Gold
Source & further information:Vintage 1970s Silver Foil Art Wall Decor Piece
The third way the foil was used was to etch the entire picture into the foil and not print on top of it. That produced examples like these:
Source & further information: Vintage 80s Gold Spiral Optical Illusion Art Vintage Gold
Source & further information: Vintage Pisces Zodiac Gold Foil Framed Art 70's Astrology
You would need to examine your pictures to see whether they contain a printed image on top of the foil, like the second case, or are done entirely in the foil, itself, like the third case.