How do I load inage from URL in preview mode?

Is it a remote URL? If so, the cross-domain stuff applies.

If it's a local URL, it's tricky since your game is not actually uploaded. Requesting something like "image.png" will send a request to "preview.construct.net/image.png", and your image does not exist at that URL. Normally you can just use sprites and tiled backgrounds anyway, loading a local URL seems like an unusual thing to do when you can just embed it in the game.

That would be a cross-domain image then, so the usual CORS stuff applies.

Hi. The Desktop Build has it disabled, so you can use this to bypass the CORS policy.

The image on cloudfront.net does not send an Access-Control-Allow-Origin header. So no, it's not correctly configured. You can check the headers it sends in the networking panel of browser dev tools.

So just to clarify. The Access control stuff ALSO has to be on the server that I wish to get the image from?

So its completely out of my control really and I cant just download images from any random URL??

Yes. It is only used on the server responding, it doesn't apply anywhere else.

This is an essential part of security on the web. For example, it prevents random websites obtaining your Facebook profile picture without your permission.