I haven't ever see those things before... for me, the trophies are enough, especially when the plot is over.

I'm not sure if you can use images from yahoo but you won't get in trouble for trying. TNT will just tell you you can't.

My personal guess would be that it should be fine. As long as it doesn't include a link to a non neo site, it should be fine. Remember the image name has to end with an image tag like .jpeg, .jpg, .gif... etc. If both of those are OK, it should be fine (provided yahoo allows it).