I assume the link you tried to copy was something like this:

https://static.wikia.nocookie.net/peanuts/images/5/5c/19880429.gif/revision/latest/scale-to-width-down/600?cb=20150823191906

Anyway, the magic of hotlinking, those attributes would control the image size but would make it not work properly in textile/HTML embedding.

Put in imgur with a link to the wiki for convenience.