After 4.7.3 update display error of single pixel image

The latest version of WordPress appears to be parsing images differently and now causing an error on our site.

The original site is rather dated, it is in the process of being re-written, and uses a single pixel image “px_grey.gif” as a spacer like this:
<img src="http://www.spadental.co.uk/themes/spapractice/images/px_grey.gif" width="148" height="1" />
ie expanding the single grey pixel to create a grey line.

Following the WordPress update these images are not being displayed, instead the browser “missing picture” icon is displayed.

If you try and display the image directly from the site with this command
https://i0.wp.com/www.spadental.co.uk/themes/spapractice/images/px_grey.gif?resize=148%2C1
You get the following message:

Sorry, the parameters you provided were not valid

What has changed and how can I correct it – the present site will only be active for a few more weeks so this is a temporary fix.

Thanks