Sure, what could be a better description of this:
than:
not visible by the naked eye, as they float very high in the atmosphere.
...
balloons ... much smaller than the one you've inserted into your post. They are very small and they are very hard to see without the use of a telescope. Even if you do happen to see one, they are coated in mirrors so that they reflect light and the environment around them making them almost impossible to spot unless you're looking for a very specific glare.
In a sense, we are in uncharted territory however. That image
wasn't on the first page of google results for "UFO", so Vaux is clearly stepping up his game.
It
was from a Hungarian science fiction site, though, so it's not stepped up that far. The extremely dark shadow suggests the steam train toy (or UFO!) is pretty close to the ground, rather than being photographed at high altitude through a telescope, as does the contrast and lack of haze.
The metadata for the camera or scanner is missing, possibly it's a very old or uncommon bit of kit.
Possibly it's been stripped out, which I doubt, as this doesn't seem like a serious effort at creating a convincing hoax.
Possibly the picture has been copied and recopied so many times and so many ways that one or more of those reproductions didn't retain that data - somewhat likely, as it has been recompressed at least once since it was taken and it's had some crude level balancing or artificial sharpening applied to it. However, google's only seen it once in one place, so it can't have done the rounds too much.
Where did you find that, Vaux, and what did they claim it was? Any suggestion where it was taken or other details?