If you have an image on your computer , you can click and drag it your website page or you can use the upload option.
If you copy a file to your clipboard, you can use the shortcuts Ctrl +V (PC) or Cmd +V (mac) to paste the image on your webpage.
Warning: You will notice as you try to resize your image, the image starts to auto crop itself to fit within the grid lines Google Sites has set. I have found this to be a little frustrating, and I hope this is something they plan to improve upon in future updates. If you really find that it can not work for what you are trying to do, you can look at the option of putting your images on a Google Drawing and then embedding this file on your website. Click here to see a page on this website where I did that. As a viewer I don't think you could even tell that it was a Google Drawing. Best part is if I make any updates to this Google Drawing, you will automatically see the updates on my website.
Please consider using the Alt text option when adding images as this is extremely helpful to those who must use a screen reader.
Just type in a brief description of your image and click Apply.
Group text, images and other items vertically