Sometimes it is really annoying to find a picture that is in the right size.
The best thing like DB~Valet said is to resize it yourself. Either use imgur (they have some easy tools for that), or get a graphics program like GIMP which is free.
Honestly it's going to be too much of a hassle to detect when you added a link to an image and resize that image for you (and it's never going to work in all cases). So I'd prefer you just linked to the image, or didn't have an image at all.