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I recently spent some time looking at the backlink profile of a leading UK food & clothing retailer and noticed that a high number of their backlinks for very competitive search phrase's consisted entirely of image backlinks. 50% of the links contained no alt text and other 50% contained a mix of just the targeted keyword or a phase containig one mention of the targeted keyword. Has anyone had any experiance of this type of marketing producing any positive effect on SEO or search engine rankings?