does any one know how do delete a spam image from an group?

Well, it takes a while for a spam image to go away but I could report it, too if you like? :)

Post the link, and people will report it, too. This may help to make it quicker.

Reporting the image itself usually gets it removed quite quickly. Reporting the member who posted it can get that account closed, especially if they spam repeatedly. I don't know whether more than one person needs to report for this to work though - I know that's needed for broken videos and links, but not whether the same applied for all reports.