Project 7: Rebuilding an Image Header (10 Points)

What You Need for This Project

A Windows machine, real or virtual
I did it on the Mac in a VMware Fusion virtual machine running 32-bit Windows XP Pro.
A hex editor, such as HxD

Right-click the link below and save the file on your desktop:

Using HashCalc or some similar program, verify the MD5 hash of your downloaded file. The correct hash value is shown below:

On your desktop, double-click the badheader.jpg file.

You see an error message, as shown below:

Open the badheader.jpg file in HxD.

If you don't have HxD, download it from: http://mh-nexus.de/en/hxd/

The header looks wrong--it starts with DE AD BE EF, as shown below:

So to fix it, you need to find out what a good JPG header looks like.

You can use online resources like this:

From http://www.garykessler.net/library/file_sigs.html

But a simpler way is to just examine a good JPG.

Open Paint.

Draw or scribble something, as shown below:

Click File, Save.

Save the file as a JPG.

Open the file you just created in HxD.

The first few bytes are different--not DE AD BE EF, but FF D8 FF E0 as shown below:

In HxD, with "badheader.jpg" open in the left pane, click on the first byte, which now is DE.

Type over it with FF

The changed letters turn red, as shown below:

Continue in the same manner to fix the first four bytes of the file in HxD.

Your file should now look like the image below:

In HxD, click File, Save.

On your desktop, double-click the badheader.jpg file.

The image should open correctly now, showing a wooden window frame with a cat looking through it.

Make sure the image of a cat is visible.

Press the PrintScrn key in the upper-right portion of the keyboard. That will copy the whole desktop to the clipboard.

YOU MUST SUBMIT A FULL-SCREEN IMAGE TO GET FULL CREDIT!

Open Paint and paste in the image.

Save the image with the filename "Your Name Proj 7". Use your real name, not the literal text "Your Name".

Email the image to me as an attachment to an e-mail message.

Send it to: cnit.121@gmail.com with a subject line of "Proj 7 From Your Name", replacing "Your Name" with your own first and last name.

Send a Cc to yourself.

There's still another bad byte in the header--the J is missing from JFIF. But it seems not to matter to Windows Photo Viewer.

Last Modified: 1-25-13 7:18 PM