You can create your own images from scratch using your favorite drawing software or you can use any photo, drawing, or other image file. Icons are square, so your image should fit well into a square. If it’s too long, the icon will likely look squished. If you are creating Mac OS X icons, 512 x 512 may look better.
This guide uses GIMP, since it’s free on all operating systems. The process is very similar in Photoshop and Pixlr.
Quick Mask allows you to select part of an image. You can use a different selection tool if you prefer!
For example, if you have an image of a phone lying on a table and want to use the phone as the icon, erase the red layer from the phone only. Use the Tool Options tab in the Toolbox window to adjust your eraser size. You can also zoom in to ensure that you erase exactly what you want. When you erase the mask, you will only be removing the mask, not the image beneath it.
Use the Offset values to center the image in your new canvas before clicking the Resize button. Once you’ve resized the image, right-click on the layer and select “Layer to Image Size”. This will change the layer boundary to match the canvas size.
Duplicate the layer 5 times. Right-click the original layer in the Layers window and select Duplicate Layer. Repeat this until you have 4 copies of the original layer, 5 layers total. Scale the original layer. Right-click the layer and select Scale Layer. Change the image scale to 256 X 256 px. Then click Image → Fit Canvas to Layers. (Note: if you are creating the icon set for OS X, start with a 512 X 512). Scale the 4 copied layers to the following sizes: 128 X 128 48 X 48 32 X 32 16 X 16
Check out our guide for changing the icons on Windows. See our guide on changing the icons on your Mac OS X computer. You might need to use a free online converter to change the ICO file to an ICNS file (Mac’s icon file format).
