How many faces do you see and which ones are at the front and which ones are at the back ?
Source unknown 

This basalt sea-cliff on the island of Heimaey in Southern Iceland looks just like a giant elephant or wooly mammoth dipping its trunk into the sea.
Heimaey is the largest island in the Vestmannaeyjar archipelago, which is a geologically young set of islands formed by volcanoes. Eldfell, a volcano on Heimaey, erupted in 1973, prompting locals to pump cold seawater onto the resulting lava flows in a successful attempt to redirect it from their harbor. The elephant on this island’s coast that attracts visitors is also formed from the volcanic basalt found everywhere on this island. Source: BoredPanda

A few strange things going on here. Sit back in your seat so you are not too close to the screen. Then look directly at the center green square. Firstly the sides of the different squares start to deform, secondly a ghostly circle appears around the green square. And, by the way, which green square is the biggest?

Hover to invert

Stare intently at the center of the left hand circle for 30 seconds and then look at the right hand circle.

This great photo by Dennis Hodges gives an illusionary look at the buildings of Manhattan. It takes a short while to get your head around the perspective but eventually it can be seen correctly.

I'm not sure what is going on here. If click onit and make it larger I can see moving lines and changing colors. How about you? Source unknown

Is this an apple tree or an orange tree. The only way to find out is to stare at the red dot for thirty seconds and then look at a white wall or ceiling and maybe keep blinking.

This fish illusion has been floating around (see what I did there) for a few years but until now never made it into the Optical Spy database. Source unknown

Stare intently at the white dot between the Green & Red tiles for 30 seconds and then look at the white dot between the dunes. Source TEDTalks