Official Artwork Releases question.

Hey there.

Every now and then on forums/image boards i see some pictures posted which are very high quality images so i guess they are official artwork. They also usually have some text (in Japanese so a poor Brit like me can't read it :P) in the corner which is distinctive of these images.

here is an example i uploaded.

I've only checked one or two of the anime's official websites but even when clicking all the links randomly i have found nothing.

Basically i am just wondering if anyone knows a place where these images are released officially or just by fans etc.

Thanks for reading.