These are "Triplet" 3D pictures, Left + Centre picture are
for parallel viewing Right + Centre picture are for cross eyed
If you can see "Magic Eye" pictures, you can see these in 3D, use the same technique to look at the left and center pictures together, merge the two pictures and they will "Snap" into 3D.
This is called "parallel" viewing, however you are limited to the size you can view, much bigger than this size and it doesn't work.
The only way to see these at full size is with the "Cross eyed" technique, this takes practice and you need to go
"Cross eyed" and use your right eye to look at the center picture, and your left eye to look at the right hand picture.
The volunteer run Bluebell Line was the UK's first preserved standard
gauge passenger railway,
re-opening part of the Lewes to East Grinstead line of the old London Brighton & South Coast Railway in 1960.
Since then it has developed into one of the largest tourist attractions in Sussex,
yet it still remains true to its objectives of the preservation for posterity of a country branch line,
its steam locomotives, coaches and goods stock, signalling systems, stations and operating practices