Lens hoods attached to super-zoom kit lenses contain a shadow monster that is released when exposed to light from the built-in flash. Remove the hood to avoid letting the monster escape into your photos.
@mattdm, @dpollitt, @YaoBoLu, and @JohnGleeson are all correct. Light from the built-in flash hitting the lens hood casts a shadow. If the lens is large enough, it may cast a shadow on its own without a hood. You have many options to try avoiding the problem:
- Don't use flash.
- Remove the hood.
- Use a smaller lens.
- Zoom in or out until the shadow isn't visible.
- Re-orient the camera so the shadow doesn't fall on a foreground object.
- Use a larger on-camera flash.
- Use an off-camera flash.
- Point the flash at a wall or the ceiling. (Some built-in flashes tilt.)
- Use a diffuser to soften the shadow.
- Use a bounce card.
Here's a before and after using a business-card bounce. A larger card would have been easier to use. The bounce was pretty weak, but not hopeless. Used +3 EC to compensate. (The 2-cent flash diffuser works better.)