You get this error when the image you’re trying to upload is too large.
The easiest way to fix this is to use Shopify’s own online image resizer here.
Simply upload the images to their online tool and select your preferred size. Then your image will be resized and you can download it and re-upload it to your Shopify store.
You can also use Paint if you have a Windows computer. Right click on the image and select “Open with Paint”. Then select resize from the toolbar and type in number equal to or less than 2048 px. Make sure “Maintain aspect ratio” is checked to avoid distortion.
Here are some other online tools you can use for resizing your image:
Just remember to make your width and height less than 2048 x 2048.
Lastly, if you’re looking to just optimize your image size but not resize it, I recommend ImageOptin (available for Mac and Online).