The flag isn't white. As bloggers have noted, the contrast on this photo has been punched up to turn light blue into white. The UN helmets which are actually light blue, seem white with slight shadows. The "white" flag is actually a back-lit, blue, UN flag. Confirmation of the doctoring of this photo is that the background of the poster in the upper right has entirely disappeared, so its black words seem to float in a "white" sky.
Yeah, you can see the washed out UN logo on it.
The part that looks photoshopped to me is the entire tank; looks like it was artificially just set in there.
This isn't a 'doctored' image in a nefarious sense. This is an image where there is an intense lightsource behind the foreground and in order to bring out the details of the foreground they had to do some dodging (lightening) or levels adjustments.
I've done photoshop work for 16 years and all they've done is make the image more presentable. They chose the image because of the content.