Taking pictures would require a great deal of factors to take into mind in order to have a great output. There is the shutter speed, the exposure, the light source, balance, and a whole lot of other stuff that contributes to a good looking picture. Even with world flags, getting a good picture would entail some of these tips:
Focus is one of the most basic and most essential factors that contribute to the intended output. World flags should at least be the main focus unless they are needed as background. Being the focus, try to make sure that the flag should be well see, and without obstruction.
Keep the picture alive and not staged. As much as possible, try to get a good picture of your world flag with normalcy in the background. In this case, have people in the background walk by perhaps, or interact with the flag itself. Also, do not overdo the interaction so as not to make it the very thing that you are trying to avoid.
Consider the colors of the world flag. Since the colors and designs of the world flags are the distinctive marks, it is very important to consider mixing colors in the fore and background so as not to blend the two together. Also avoid hot contrast colors such as red and blue or pink and blue that would be straining to the eye.
A combination of these, plus a good lighting source that would be able to show the wider space of any world flags would merit anyone a worthwhile picture of a flag that is pleasing to see.