The image on the left probably looks like a dent (concave), while the image on the right probably looks like a bump (convex).
These two images are simply flipped copies of each other. The reason they look different is that your visual system is inclined to interpret images as having a light source coming from above - the shadows from such a light source are only consisent with a dent (left) and bump (right). Drag your cursor over the images to flip the images (and the percept).