Where reuse of an image is permitted, often you are not allowed to alter the image except to resize it.
DOWNLOAD YOUR OWN COPY OF IMAGES! Where reuse is permitted, do not display the image on your site by linking to it from this site. Often the same restriction will apply to the credited source site. Unless specifically stated otherwise, you must download a copy of an image from the credited source (where permitted), or from this site (where permitted), and upload it to your own server.