Linking to images on other websites is called hotlinking.
Can i load images from other websites and display into my website?
Yes. But the other website could (try to) block you.
Is loading the images from other sites into mysite is good?
Not really. Good for who? The site you are hotlinking images from would probably not like it. (Whether it actually helps the external site SEO-wise is debatable - I thought there was a another recent Webmasters question relating to this specific point, but I can't seem to find it?)
Will it affect my website in anyways like speed, seo, copyright?
The good things from your point of view:
- It doesn't cost you any bandwidth.
- If the external site is fast (or located near to your users) then it might even improve your perceived site speed.
- The image it out of your control. The external site could block you or change the image at anytime without your knowledge.
- The image might indeed be copyright (as with any image). So, you could potentially face legal issues.
- If the external site is slow then your site is slow.
- It won't do anything for your SEO.