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I would stick with the image embed option and live with the fact that not everyone will link.  I'd rather have more people posting my advert.... sorry, widget on their site that included some without links than I would have less people using it.    The vast majority of people will take the easy way anyway. I'm not sure that adding a registration would really help anyway. What I would say is be careful not to "over optimise" your anchor text doing this.  It is surprisingly easy to skew your anchor text in a dangerous direction with a good widget campaign.  You could even consider mixing up the anchor text that you offer them as part of the widget generation, but generally I would err towards brand over keyword.