What size should the page images be?

There's no strict size imposed for the images you plan to use on your form. The general rule of thumb is to use an image size that is "ideal" for your needs.

For example:

🔘 If you will place an image on your header, use something that is short but wide

🔘 If you will place a background image to the entire form, use something that is relatively bigger than most viewport/screensize

🔘 And so on...