Im not the person who posted them, but I can tell that their filenames are from pixiv. If the name is a 7-8 digit number its usually from pixiv.

For example, 45625938_p3.png would be the 4th picture of a multi-picture upload. 36672827.jpg is from a single picture upload.

I keep this link bookmarked, for when Im looking for sources:
http://www.pixiv.net/member_illust.php?mode=medium&illust_id=

If you add the number from the file name to the end you will usually get the source, if the artist hasnt deleted the picture.

http://www.pixiv.net/member_illust.php?mode=medium&illust_id=45625938
http://www.pixiv.net/member_illust.php?mode=medium&illust_id=36672827