I got a solution. First you need to upload the image to the "Download" area. After that, enter the image URL.
<img src="http://yourgoogleproject.googlecode.com/files/name of your image.PNG" alt="Logo"/> You must paste the above code into apostrophe (') and end with an apostrophe and you can paste this into project description tab of the project summary tab (I just added here in my case)
The downloaded file will automatically go to the "files" folder of your project.
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