Hi Phill, I haven't seen that problem before. What format is your image file (JPG, PNG)? Have you tried selecting it anyway, and see if it appears okay on the site? Have you made sure that the uploaded image has the same file size as the local version?
If you want to test if the image is somehow corrupted or incompatible with your web browser, you could create a local HTML file like this, put your image in the same directory, replace the image file name, and open it with your web browser:
<!DOCTYPE html>
<html>
<head></head>
<body><img src="my_image.jpg"></body>
</html>