I'll break it down.

1. When done with your guitar hit the prtsc button on your keyboard.
2. Open paint and paste in your image.
3. Use the select tool to select the unwanted stuff from the image and cut
4. At this point you'll have your guitar image surrounded by a white screen.
5. To get rid of the extra white, Select the guitar image and copy it.
6. Open a new paint window. Paste the guitar image into it.
7. Now it is just the guitar image. Save AS a jpeg file.
8. Upload to photobucket as you regularly do.