Edit: 1/24/2015

New Evidence: Confirming it's a fake. 

The dimensions of the PlayStation 4, as mentioned in the official specification sheet released by Sony, is 275×53×305 mm. This means that the PS4 has a width of 275mm. The size of a standard Blu Ray disc that the PlayStation 4 uses is 120mm. With those numbers in mind, a Reddit user estimated the width of the alleged PlayStation 4 Slim.

As shown in the image below, the user estimates that it comes out to be 166mm. The size of the Blu Ray player comes out to be 84.17mm, which means there is no way that a standard Blu ray disc will fit in this design. Now there are smaller sized discs available (80mm) but they are capable of holding only 15.6GB. In short, the alleged PS4 slim won’t have a big enough Blu Ray drive to accept games disc. This  proves that the design is nothing but fake with ridiculous dimensions concept.

Source: http://gamingbolt.com/this-is-why-the-recent-ps4-slim-leak-was-ridiculous-and-fake#i1cDgt5t0VJU3Mja.99

Original Story

There have been many reports/speculation on the internet about PlayStation 4 Slim already being in development at Sony, and an official announcement might happen at E3 2015 or at GamesCom 2015. Today, on Multiplayer's Italy website, the first image of "PlayStation 4 Slim" was leaked, according to the details in the image, PS4 Slim might be internally code named as "Monolith".

Gamepure

For comparison here is the PS3 to PS3 slim: Everyone thought the leaks were fake and they turned out to be true.

For comparison here is the PS2 to PS2 slim

Source: http://www.vg247.it/2015/01/22/ecco-la-prima-immagine-di-playstation-4-slim-oppure-no/

English Source: http://www.gamepur.com/news/17745-first-actual-image-ps4-slim-model-leaked-pretty-small-size-compared-current.html

Edit: Special thanks to BraLoD for the correction, new news has arrived that logically concludes this Slim is a fake.

nah, this is too easy to do in photoshop. first picture looks totally photoshopped. this doesn't shoot down the 'story,' but i doubt we'll see one within a year and some change of the ps4's release.

Looks sooo tiny! I would be worried about the airflow tbh if that is the real one

Angled would be challenging.  That being said with 1 8GB sticks, smaller motherboard, and possible die shring.  The timing is about right.

Die shrinks generally have less heat, less memory modules will lower heat, cost revision already lowered some heat, it could use less electricity meaning smaller power supply less heat, and who knows it could have an exsternal power supply. 

"CONFIDENTIAL" = made up

That looks cute. But could be just one of many possible designs. Or a fake.

IF this is true, that's really fucking small.

We have had a lot of "Confidential" leaks end up being accurate this gen.  The posibiliy is there.  It could also be a prototype.

If it had an external power supply then I wouldn't see an issue, it would probably be cooler than the current unit.  With an internal power supply I would doubt i would be reluctant.

Could it also mean a price cut? :)

There is NO way that it is that tiny compared to the original. That would just be epic but I doubt it.