Do you think you've got good vision? Then we've got an optical illusion challenge for you.

Hidden in the image above is one four-letter word that is slightly different from all the others.

The challenge is, can you spot it in less than 15 seconds?

Optical illusions such as this one, created by Freshers Live, are great for keeping the mind and eyes active.

We've put the solution a little further down the page, but if you have not managed to solve it yet here is the challenge again.

If you need a hint, then you're looking for the word 'seal' hidden amongst the word 'zeal' written dozens of times in perfectly straight rows and columns.

The illusion works because people's eyes are used to just skimming over images - meaning it is very easy for minor details like this to be overlooked.

Not found it yet? Here's the solution for you...