LEVEL: VERY EASY
Note: The image was not generated with any steganography tool.
Note2: In this case, the message can be extracted without coding.
Hint 1:GIMP is your friend
Hint 1.5:Use the Color>Components>Decompose to get the image components separated.
Hint 2:PGM format saves grey scale images as raw data
Hint 3:The image is pretty blue, isn’t it?. Take a look to the colour components
Nice weekend!
What an hard thing !
The most i can get is that i need a sort of blue filter to put on top of the image, but i just don’t how to make this 
Then, you have to open the first Hint 
I downloaded it, opened GIMP, decomposed it, took out the red and the green, and now I’m staring at a grayscale of the blue image, but I don’t know what to do next.
man ppm
Check the SEE ALSO section, the format to use is listed there
Arrrrg this make me mad 
I can now see some letter (i’m playing with some gray levels on blue channel) but no idea how to get the perfect result 
PS: How can i hide my words in order to avoid spoil ?
@Acarnage
Use [spoiler] ... [/spoiler]
Finally Done !
Just Wow ! A great thing i learned today !
Congrats!.. Next one will be more difficult
Got it finally! Any chance you could show us exactly how you created the image? I see there is a PNM filter mentioned in the message.
Sure. I generate the image with a small program I wrote. I do not know if it is possible to generate the file just using a image processing tool. I will post the code later anyway a bit later today (I’m finishing something else).
Hi. New to site. Love the challenge. Still trying to complete it. When will you post the code?
Hi @spoclate and thanks.
You can find the solution here