Create a free mockup in 10 simple steps
Sign up or Log in to your Canva account.
Click on "Create a design" (top right corner) then click "Custom size".
Add the size of the image you'd like to generate (e.g. 2000x1000px)
Upload/select the image file you'd like to use in your mockup
Click the Image  > Effects  > Smartmockups  (select "See all").
Once you've chosen/adjusted the one you want to use click download
You're all done. Enjoy!
Create as many mockups as you wish but don't overuse it on your website because your business will feel "too stock" and customers won't like this.
Here is a few more similar websites you can use for more FREE/Paid OPTIONS (frames, mugs, shirts, billboards, computers, walls, logos...)