One thing you can do if looking for an image is to save and/or link a thumbnail of said image. If you're using something like Photobucket or Google image search, viewing the thumbnail should give a good idea of whether it will be distinguishable at a smaller size. Example:
thumbnail and
fullsize (Granted, the fullsize for this isn't all that large.)
Don't link only the thumbnail, though, as there are more intelligent ways of reducing the size of an image than thumbnails grant.