The cache is not at the given coordinates, which are for Moorfield Eye Hospital.
The pictures are autostereograms. If you are interested you can read about them here.
The coordinates are visible in the picture when you look at it in the correct way.
To do this you need to look through the picture, as if is transparent and you are looking at a point in the distance.
At first the image will be blurred but after a few seconds your brain will process the image to reveal the numbers hidden within.
The difficulty is hard to judge because you will probably find this very easy or very hard.
Northing:
Westing:
