Like we've all said, it's perhaps a little big at 300px, give or take. Resizing the images would be a pain so I wouldn't go that route, but I'm not sure what you can do to be honest, as I'm no signature professional with my probably-slightly-over-the-limit signature.
Unless you can find a way to make those spoilers take up less space, I'd leave it the way it is for now as it's not hugely over the limit of this loose rule.
If others complain that it's too large, the easiest option would probably be to keep those links under the image but move the spoilers beside the image using a table since then it would take up less vertical space and make use of some of that blank horizontal room you've got there!
Example:
[table="width: 700, align: center"]
[tr]
[td]
Hey look, a link![/td]
[td]
[/td]
[/tr]
[/table]
HTML:
[table="width: 700, align: center"]
[tr]
[td][IMG]http://rs950.pbsrc.com/albums/ad348/donnalim/1.gif~c200[/IMG]
[URL="http://google.co.uk"]Hey look, a link![/URL][/td][/td]
[td][SPOILER="Spoiler 1"]Sample text[/SPOILER][SPOILER="Spoiler 2"]Sample text[/SPOILER][SPOILER="Spoiler 3"]Sample text[/SPOILER][/td]
[/tr]
[/table]