I uploaded the jpg file to arcgis online and try to set the image url to background image for Web page . i am getting Invalid image Url
When adding an image as the web page background in Survey123's Web Designer, ensure the image item is shared correctly and that you're using the URL that can be copied in the bottom-right of the item details page (not the URL of the item details page itself):
For more on this please refer to the "Making image assets available to Web Designer" section in this useful blog:
Retrieving data ...