Recently, I had changed my tab icon of my blogger site. It used to be a common blogger icon which is an orange square with the white letter B inside it. I changed it into my custom made icon of two linking Cs similar to my banner. If you are interested in doing the same, here are the steps to do it:
1. Prepare an image, can be JPG or PNG format. I suggest PNG format because its size will be smaller by a 4:1 ratio. It means that a 10 Kb JPG image will be a 2.5 Kb in PNG format. Also make sure the size is small like 20 x 20 pixels or less, so the file will be smaller in size and won't make your blog loads slower.
If it's difficult for you to edit a small image, you can make a bigger one first, like 200 x 200 pixels or more, and after finish, you can skew it smaller. Microsoft Paint can do it for you easily.
2. Upload the image to an image hosting service, like the free Tinypic. Then, obtain the direct link to your image for the next step.
3. Add the underlined tags to your template. To access it, click "edit html" in "layout" section. Put them in head section, between "title" tag and "b:skin" tag. If you face difficulties in finding the tag, just use the find tool in your browser. In Mozilla Firefox, the shortcut is ctrl+f. If you use another browsers, apply with adaptation.
<link href='put the direct URL of your image here' rel='shortcut icon' type='image/vnd.microsoft.icon'/>
Save and done!