HELP PLEASE! I think this is a relatively easy image swap solution but for the life of me I cant seem to get it.

HELP PLEASE! I think this is a relatively easy image swap solution but for the life of me I cant seem to get it.

Hey everyone,
I must say this community has proven to be not only incredibly knowledgable, but also amazing people on here, thank you all! :)

Here is the newest issue I have, 

I have these set to reveal on hover, just using some css. but now they need to stay revealed until the next one is hovered over. 

I am guessing that this will be a onMouseOver event without a onMouseOut to reset them but I have not been able to implement successfully.

here is a fiddle to show how it functions currently( html and css only).

thank you all,
Jeff