Tutorial: Editing Images with Audacity
Audacity is a free and open-source digital audio editor. You can also use it to create some cool effects on digital images, though. Scroll down if you want to see examples; read on to learn how to do it yourself! :)
Note: You don't need to be extremely technical to use this tutorial, but if you do not have any experience with Audacity you might have trouble. This is a tutorial for how to use Audacity to edit images assuming you have some experience with editing audio in Audacity, not for how to use Audacity in general.
Step 1: choose a picture and open and resave it as a BMP in Paint.NET or GIMP (or something else).
If asked for any settings, the default should be perfect (at least in all my tests :p).
Step 2: open Audacity.
Step 3: Click File -> Import -> Raw Data...
Step 4: Double-click the file you want to edit and wait a few seconds.
Step 5: Put Encoding to 'A-Law', Byte order to 'Little-endian' and Channels to '1 Channel (Mono)', and click Import.
Step 6: You will now see your image as sound. Try playing part of it back. :D
Step 7: You can now apply audio effects to your image. However, there is one part that you should not edit. Zoom in on the very left part of the file, until you can see the individual samples, represented by dots. You should not edit anything that comes before the second dot before the 0.00080 mark. The samples before this make up the file header, and if you change this, you will not be able to open your image anymore.
If you want to edit your entire image, start your selection from that dot. It is sample 34.
Advanced Tip (you can skip these at first) 1: When making your selection start at sample 34 or when attempting to merge multiple pictures, you have to be really precise. To make this easier, you can change the options at the bottom of the window to display values in samples instead of hours, minutes, seconds and milliseconds. Also change "Start and End of Selection" to "Start and Length of Selection", which will make it possible to experiment with replacing data of one image by data from another (the length of the file should stay the same, this is why you need such precision). You can change "Snap-To" to "Nearest" or "Prior" to more easily be precise with the mouse, but it is probably better to manually enter in the values with the keyboard.
Advanced Tip 2: Editing specific parts of the image can be tricky. There are ways to calculate what's where in the file, probably, but I haven't gotten so advanced myself yet. :p Good to know however is the following: the image is made up from right to left, from bottom to top (so the opposite of reading direction). Thus, if you want to change the top of the picture but not the bottom, you should edit the latter half of the file.
Step 8: Apply audio effects! There are plugins for Audacity adding more effects, but the basic effects should be quite enough to play around with already. For this example I will be amplifying the entire image (besides the header, the first 33 samples!) by 3 decibel.
Step 9: Press Ctrl + Shift + E (you can also use the toolbar but this is faster :p). Now here are lots of settings that need to be right: set "Save as type" to 'Other uncompressed files', set "Header" to 'RAW (header-less)' and set "Encoding" to 'A-Law'. Give your file a name and end it with ".bmp".
Step 10: Click 'Save', 'Yes' and 'OK'. :D
You can now check out your image in any image viewer!
After exporting your image, you can press Ctrl + Z to undo your changes and try again, or restart from step 1 or 3.