We begin with the two photographs from the question, showing (1) the optical system and (2) looking back along the optic axis of the system at the original object, which we call O1.
The first image: Image I1 will be on the opposite side of the lens at the same distance from the lens as the object O1, will be real, inverted, and have a magnification M=-1 with respect to O1. It can be observed by removing the mirror and placing a screen at the position of the image. The image is photographed at the left below, looking forward from above the source along the optic axis. Note that the image is in fact inverted; the camera is turned around, looking in the opposite direction. The mirror has been removed and placed at the left of the optic axis (as seen in the photograph).
The second image: The image I1 serves as the object O2 for the reflection by the mirror. The mirror then creates an image of object O2. Because this object is behind the mirror, it is a virtual object. In order to photograph this object the mirror was tilted slightly upward so that its optic axis was aimed above the lens. Note that image I2 is at the same location as O2 but is inverted with respect to O2. The magnification M=-1: the image is at the same position as the object, but is inverted.
The third image: The virtual image I2 of object O2, behind the mirror, then acts as the object O3 for the production of final image I3 by the lens. Because O2, and thus I2, are behind the mirror at the same distance as I1, the lens creates an image I3 at the same distance to the right of the lens. This is shown in the photograph below. Image I3 will be inverted with respect object O3, which makes it inverted with respect to the original object. This can be seen in the photograph below, which compares the final image with the original object. In this photograph the mirror has been tilted slightly upward so that the image is above the original object. As in the case of O1 and I1, the magnification M=-1, as seen in the photograph.
For a more detailed analysis, please see set of ray diagrams and concomitant calculations that show the progression from the original object to the final image, available in Microsoft Word or Adobe PDF format.
I used this question in a physics for engineers course some time back. After the students turned in their tests, they were allowed to go behind a curtain and see the actual experiment.
