It is most likely diatoms. Not an uncommon problem in new tanks. People are tempted to start buying chemicals to clear it up or disrupt the tank and such. Patience is warranted and if you let the tank mature naturally then there will be micro-fauna that develop and compete with diatoms for nutrients and they will literally go away over nite. In an undisturbed populated tank this usually occurs in a few weeks or so after they make an appearance. Some ways to help keep them to a minimum is to make sure you are doing small partial water changes frequently, feed sparingly, make sure you have adequate water movement throughout the tank. And if you keep the light on more than 8 hours a day or o you should cut it off.
Honestly though, looking at the picture I do not see any appreciable problem.
Bill