So I recently made a site for my wedding and my soon-to-be-father-in-law, Bob, told me that he couldn't see the banner in IE 7. At first I thought maybe it was a problem with IE 7 displaying background images set through CSS. So, I removed the background image from the div and put the image inside the div. I should've known this wasn't the problem since the background image for the page was showing up fine.
At this point I did what anybody else would do. I searched Google with everything I could possibly think of. Unfortunately, I couldn't find anything even remotely helpful. At this point, I got Bob on the phone and just started hacking away at my site and having him refresh after every change. I tried defining the width on the div and when that didn't work I defined the height and width on the image. Still nothing.
Then I tried adding some alt text (it was set to an empty string since it was just for decoration) to see if the browser was at least trying to render the element. Nothing. I put text before and after the image and Bob said he saw just the text, with no hint that there was an image between the words. Okay, something's seriously wrong.
I asked him to go directly to the image by typing in the URL manually. Blank white page. Hmm...try the image directory listing. Here comes the first clue. The directory listing is complete, but the file name for banner.jpg is missing. The icon, modified time and size all show up, but no name. Unsure of why this is happening, I re-save the file and upload it again. Same problem. To rule out a problem with an oddly corrupted file, I save the file as a PNG and upload. Same problem; both banner.jpg and banner.png have no file name in the directory listing for Bob.
The obvious next step was to try a different file name. I renamed banner.jpg to header.jpg and it magically showed up in his listing. I went ahead and updated the site to use header.jpg and the site started displaying properly for him. After digging through pages upon pages of search results dealing with "banner," "file," "name" and "ie7" I finally found a thread that linked to an informative page.
Norton Internet Security has an ad-blocking feature, which is defaulted to being on. This feature looks for things that it suspects to be ads and completely blocks them from the user, as if they didn't exist. Apparently, having a media file named banner meets the criteria for being an ad. It just so happened that the only computer Bob had Norton Internet Security installed on was the one that had IE 7. Go figure.
For more info, check out The New Ad Blocking Debacle. Interestingly, this was posted in March, 2004; I'm amazed I didn't hear about this earlier.