My pictures from Grant Park (warning...a lot)

"Due to the size limitations of the modern compact and ultra-compact cameras, especially digital cameras, the distance between the lens and the built-in flash has decreased, thereby decreasing the angle of light reflection to the lens and increasing the likelihood of light reflection off normally sub-visible particles. Hence, the orb artifact is commonplace with small digital or film camera photographs.
The orb artifact can result from reflection of light off solid particles (e.g., dust, pollen), liquid particles (water droplets - especially rain) or other foreign material within the camera lens.
The image artifacts usually appear as either white or semi-transparent circles, though may also occur with whole or partial color spectrums, purple fringing or other chromatic aberration. With rain droplets, an image may capture light passing through the droplet creating a small rainbow effect."