One of the fastest blender render farms is the one at http://render.st/ . If you need to render blender animations, be sure to check them out.

If you need to add website screenshots to your site, the best service I was able to find so far is one named pagepeeker.com.
On the same site, when paying for the services, they provide the ability to capture full page screenshots. That is a very rare service that I have not seen offered in a reliable way by any other company.

When you have a website, it's important to keep the image size as small as possible. You can check the ShortPixel image optimization plugin, which can help for wordpress sites and not only.