An image like the top image which has few changes in color from left to right results in very few tags being written. Flat-color graphics have information which compresses well with this technique. For comparison the JPEG version of this file is 116k. The GIF file below is nine kilobytes in size. The color changes for this flat-color graphic are very few when compared to a photograph.
Photos change colors at almost every pixel across.
For comparison the JPEG version of this file is 120k .