What are these rashes/blister like things on my knee ?

[michaelong]

Hi , I'm having some sort of blister or maybe rashes on me knee cap , I think I experienced this years ago on my elbow cap , but it wasn't itchy and ignored it , it just disappeared after a few weeks

http://i39.tinypic.com/vo1htf.jpg

to red spots are blood ( scratching knee while sleeping )

any idea what this is ?