Funny, but the sheep on the RH side look somewhat "pink" compared to the other sheep. You might try slightly desaturating the reds and lightening the master color for that particular layer from source 4.

You will probably also want to find another football image to use. Although the photographer on Flickr, Ed Yourdon has it available, as ALL NFL team logos are copyright and trademarked to the NFL, which forbids any redistribution or publication of their property without express written consent...

Corrected the sheep!

Thanks for the advice MossyB, I didn't thought about trademarks. I'm not a football follower so I didn't noticed the Jets logo (I know it was all over the place... )
I'm looking for another background image but it's difficult to find something that suits me. For now I've just cloned out all the logos I could see!!

I've got a question: If I use an image of , for example, a shoe and it has the logo of the manufacturer (say Nike), must I remove it? I just want to know for future works...

Entries on Pxleyes are considered "not for profit" so there is no capital gain from the trademarks nor should there be any inferred endorsement by the logo/trademark holder. Logos and trademarks are everywhere, if you take a picture of a street scene with a MacDonald's in the photo you aren't violating any copyright laws by posting that image. The determination is based on the intent of the image. In the case of the shoe with the Nike logo, if a character in the background photo is wearing the shoes that's incidental and not the main focus, but if you did a chop with shoe and logo as the focal point it could be seen as an inferred endorsement or considered derogatory or mistaken for a promotion by Nike without their consent. It's best to avoid Logos and trademarks in your work to keep things simple but don't freak out if there's a McD's in your street scene background. If you have any doubts you can contact a mod for advice.

Thank you for the explanation!!