Steve,
I'm not on my own computer so I don't have an EXIF reader here. We could make more meaningful comments is we knew your camera settings and lense length for this shot. It looks like you were fairly distant to the frog and need considerably more reach. I'm not certain a flash would help much unless you could approach it with a much longer lense- the light fall off from a flash is stunningly rapid, and I'm not certain whether its reflection would enhance or detract from the subject. If this is a really high resolution, you might just try cropping the heck out of it and see how it looks.
Thanks for the comment. It was taken about 15 feet away with an older Nikkor-reflex 500 mm lens, iso 400, 1/250, f/0. The close distance is why I thought the flash might work.