Are you asking us if it's possible to take a photo with your iMac camera and use that photo to upload to eBay and\or social media? If that's your question, the answer is yes.
To follow up on that: once you've taken the photo in Photo Booth, drag the photo from there to a folder or the desktop (temporarily) and then upload that to the service you prefer (Facebook, Twitter and Flickr sharing are all built into iPhoto, if you want to use that).
Shop for your Apple, Mac, iPhone and other computer products on Amazon.
We are a participant in the Amazon Services LLC Associates Program, an affiliate program designed to provide a means for us to earn fees by linking to Amazon and affiliated sites.