As a general rule of thumb, images should be no larger than 1,500 pixels on the longest side. However, there are a few situations where you might want to use an image that’s larger than 1,500 pixels.
If you’re planning on using full-width images or galleries, you can upload images up to 2,048 pixels on the longest side. These images will be automatically cropped to fit the width of your site content area.
If you need to upload an image that’s larger than 2,048 pixels, you can do so using the Image Block. This block lets you display images up to 5,000 pixels on the longest side.
Conclusion:
In general, images should be no larger than 1,500 pixels on the longest side. However, there are situations where you might want to use an image that’s larger than 1,500 pixels.