What are all these other pictures that appear when I view a picture from email?

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Summary: Viewing a picture from email causes the email program to place that image on your hard disk, along side other pictures from other places.

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They are images on your machine.

Understanding why they're there and how they got there requires a short explanation of how your email program handles that request to view a picture, and how that interacts with other programs on your machine.

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Anything attached in an email is actually encoded into the email message itself as, believe it or not, plain text. Even that picture that you're looking at was probably encoded as something that, were you to look at the raw email message, looks much like this:

Content-Type: image/jpg;
        name="image0018.jpg"
Content-Transfer-Encoding: base64
Content-Disposition: attachment;
        filename="image0018.jpg"

/9j/4AAQSkZJRgABAQEAYABgAAD/2wBDAAoHBwgHBgoICAgLCgoLDhgQDg0NDh0VFhEYIx8lJCIf
IiEmKzcvJik0KSEiMEExNDk7Pj4+JS5ESUM8SDc9Pjv/2wBDAQoLCw4NDhwQEBw7KCIoOzs7Ozs7
Ozs7Ozs7Ozs7Ozs7Ozs7Ozs7Ozs7Ozs7Ozs7Ozs7Ozs7Ozs7Ozs7Ozs7Ozv/wAARCAEyAr4DASIA
AhEBAxEB/8QAHwAAAQUBAQEBAQEAAAAAAAAAAAECAwQFBgcICQoL/8QAtRAAAgEDAwIEAwUFBAQA
AAF9AQIDAAQRBRIhMUEGE1FhByJxFDKBkaEII0KxwRVS0fAkM2JyggkKFhcYGRolJicoKSo0NTY3
ODk6Q0RFRkdISUpTVFVWV1hZWmNkZWZnaGlqc3R1dnd4eXqDhIWGh4iJipKTlJWWl5iZmqKjpKWm
...

Yes, that's a picture; well, the first part of it anyway; the encoded portion goes on for over 800 more lines.

The deep dark secret about email is that it can only handle text - anything else needs to be encoded into text in some way. When you view a picture, your email program has to decode that text mess and turn it back into a picture file - "image0018.jpg" in the example above.

The first question that your email program has to answer is "where do I put the decoded file?".

There are two typical answers: the file is either placed in your Windows temporary files folder, or it's placed into the Internet Explorer Cache folder. (Email programs can often be configured to place them elsewhere instead, but if you haven't changed anything it's likely one of those two.)

Using IE's cache as the example choice, when you view the picture, your email program takes that mess of text, converts it back into its original image file format, and places it into the cache folder. For example:

c:\Documents and Settings\LeoN\Local Settings\Temporary Internet Files\image0018.jpg

Now it can tell Windows Picture and Fax Viewer (or whatever viewing program you might have installed) "here's the image file to show" when you ask to view it.

So now, Windows Picture and Fax Viewer actually has two pieces of information: the image file to view is "image0018.jpg", and the fact that it's located in the folder "c:\Documents and Settings\LeoN\Local Settings\Temporary Internet Files".

Here's what you're seeing: when you navigate within Windows Picture and Fax Viewer, it's scrolling you through all the other images that might happen to be in that folder.

Your next question, of course, is where did they come from?

Internet Explorer. As you surf the web IE tries to download things only once. So if you visit a page that has a picture, and then a little while later you visit that same page, IE doesn't have to download that picture again if it's already in the cache. Which files can be kept in the cache, and for how long depends on several things, but the point is that there are likely lots of pictures in IE's cache.

And if you end up browsing around that cache because you're looking at a picture from your email that also happened to be placed there, you'll see them.

Pictures you don't recognize as having seen are often due to two reasons:

• Graphical elements used in page design. The best example is that your browser actually has no way to "make" a rounded corner. Square boxes, no problem, but fancy web 2.0 style rounded corners on those boxes require more work. What typically happens is that four images of rounded corners are used to construct the box. Those images are just ... images ... and they get placed into the browser cache like any other image or picture. When you happen to be browsing the cache you'll see them as individual elements. This actually happens on many, many graphically intensive websites.

• Blocked popups. Your browser may be blocking popups, but it might not be doing so as quickly as you think. The popup might actually start to load its contents, including pictures, before the browser gets around to killing it. Those pictures, though never displayed, end up in the cache anyway. (This is also a common cause of history items appearing for pages you've never visited - they're popups that were blocked after the history entry was created.)

Bottom line: it happens, and it's nothing to worry about. It's simply a side effect of what your email program needs to do in order for you to be able to see a picture.

Related:

• What are all these other pictures when I view emailed photos? What are all these other pictures when I view emailed photos?

• How do I make something other than "Picture and FAX Viewer" the default for viewing pictures? Windows Picture and FAX Viewer is the default application for viewing images under Windows. But there are many other programs out there as well.

• Can I delete the contents of my TMP folder? Windows maintains a folder for temporary files but it doesn't always get cleaned up. With a little care you can delete the temporary folder's contents.

Article C3639 - February 6, 2009