Wood flooring is usually installed with a gap to the actual wall - this is important, because it allows for differences in expansion/contraction between the flooring and the materials used to frame the building. If you tried to make a perfect tight fit, the floor would either buckle, crack, or pull away from the wall.
The gap is typically covered with trim (molding) when finishing the room after installing the flooring.
Problems arise when people try to install new flooring without replacing the trim. It looks like that's what has happened here, since it appears that your flooring is butted up against the trim, not the actual wall itself. The most common method of dealing with this is to install more trim, up against the existing trim - typically, a piece of quarter round molding as seen in this photo:
It appears that the photo you've posted shows a door frame. For cases like this, where a quarter round would block the operation of the door, it's typical to undercut the existing molding so the new flooring can be slipped under it. Here's a photo of a piece of flooring slipped under an undercut door jamb:
Of course, in your case, it's too late to undercut the jamb. Unless you're willing to rework the door there may not be much you can do that won't run the risk of looking like a hack-job. I would be tempted to cut small pieces of the floor material and lay them in the gaps (leaving them free-floating so they can move with the floor). Or, you could use small pieces of flooring cork (or any cork, really) or even foam rubber. Once the gap is filled, your eye won't pick up on it as easily. Caulk won't be easy to get a good looking finish with, and will likely shrink or pull away in a gap that large anyways.
If you do try to fill the gap, make sure it's with a material that can still allow for movement of the flooring.