Images not updating

I have a page where I want to post data from my weather station: cafoxweather.com

The weather station has software (weatherlink) that generates .gif images and transfers these images to an online server via FTP, replacing the old images so there is only one of each image file in the folder. I have been successful in getting the FTP to work, the images are uploading to the “wp-content” folder on my host’s server.
I was able to get the images into WordPress by entering the image URL with the “add media” menu in the default editor. The preview of the page in WordPress shows the up-to-date images but when I view the page in a web browser the images are time stamped at the time when I first entered the image URL into WordPress. Also, I can view the up-to-date images by entering the image URL in a web browser, for example: cafoxweather.com/wp-content/OutsideTemp.gif

How can I get the images to show live data?

Any help is greatly appreciated!