I would like to promote some laptop products.
For example Lets say Acer Laptop.
Am I allowed to copy image from that website and use it in my website?
I'm promoting their products. So its not illegal right?
No amount of excuses can make stealing the content of others legal. While there is something as fair use, you cannot use an entire image or other media which is created by someone else and not licensed for your use.
There are three common ways to obtain product images:
Sadly its not a matter of if your promoting a product or not, for example Video Trailers even though they are promoting a movie they still require an publishing license, as well as Lyrics for Music. This is the same for some posters and stock images of items, some companies require you to purchase a license - It's an monopoly and everyone wants their cut.