This is a raw NASA image taken by the curiosity rover at Gale Crater on November 8th of 2016.
These are our objects of interest. In stark contrast to their surroundings they immediately grab our attention.
I've cleaned up the image a bit for a better visual. It certainly looks like they could be part of
a concrete wall such as those found on earth. The smaller piece looks like a section of two cinder blocks while the larger piece looks like a cinder block retaining wall with a tiled facade. Are these the remnants of a past or present civilization on Mars? On earth nature has created some cube like structures like those found at Giant's Causeway in Ireland, but they are never isolated pieces. They are usually made of the same material and many are found together. Nothing similar to what we see here in his image.