I assume you are trying to email a picture of an object for sale to your contact. If not, please let us know.
In the browser - probably Safari - right-click (or control-click depending on your mouse) on the picture of the object.
On the context menu which appears, there should be "Save image as" and "Save image to the desktop"
Once it is saved at your end, you can attach it to an email like any other file.