Images from FTP server not updating on website

Let me first say that this is my first experience with WordPress and site building in general, but I am continually learning. I have been searching for an answer to this problem over the past few days with no luck.

I had a friend of mine start a simple, single page website for me to post data from my weather station: cafoxweather.com

The weather station has software (weatherlink) that generates .gif images and FTPs these images at intervals specified by me to an online server, 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

Any help is greatly appreciated!