My predecessor created a website for a dealer in second hand luxury cars. It has a CMS and new offers are added by the site owner. The site includes many photos of the cars. In order to have visitors see an optimal size of the photos, almost every photos is resized on-the-fly before being displayed.
By studying the visitor stats, I found out that there are a couple of car forums where the users post photos using the page which resizes the photos. The bandwidth and resizing comes from the car site. The aspx-page which does the resizing is by far the most called page in the site, it is requested an order of magnitude more often then the next most-requested page.
The site sometimes gives an Internal Server Error, which is caused - as was told us by the company which hosts the site - by memory problems. We were told to check our scripts, I did a rough check, but nothing strange caught my eye. Then I looked at the stats and thought that the resizing of images on the fly was likely the cause of the memory problems. That is my gut feeling, but I have no hard numbers about the memory cost of resizing images on the fly.
Does anyone have some information to confirm my gut feeling?