The image shown consists of 248 X 324 pixels. The original was obtained by scanning with 24-bit color resolution (8 bits each or R, G, B), requiring a total of 241,548 bytes. All compression ratios are given relative to the original.
The vertical striping you see in the sky is an artifact known as "Moire Patterns". It's due to the fact that the original was an image printed using halftones (it's taken from the CMU Undergraduate Catalog). The spacing and orientation of the halftone dots interact with the spacing of the scanner sensor elements to create an interference pattern. It would have been better to start with a photograph.
The colors information is encoded at with just two bytes for every four pixels. There is no visible degradation in quality.
Observe that this image still looks pretty good. You can see some nonuniform color gradations in the sky and some loss of detail in the brick walls and window frames.
Things don't look so good here. The sky is very patchy (you can see the 8 X 8 pixel blocks quite clearly), and things look blurry. Note the bleeding of colors.
We're really losing it. Most of the color information has been cast out, and the shape of the building is barely recognizable.
Gone! You'd have a hard time figuring what is shown in this picture, if you hadn't already seen the higher quality versions.