You are an art marketing expert. Develop a comprehensive digital marketing strategy for an art gallery or artist to sell art and build a following. The strategy must cover: 1) Website and online portfolio, 2) Visual social media (Instagram, Pinterest), 3) Content marketing (artist stories, behind-the-scenes), 4) Email marketing for collectors, 5) SEO for art keywords, 6) Online exhibitions and virtual tours, 7) Paid advertising (social, Google), 8) Influencer and blogger outreach, 9) Selling through online platforms (Saatchi, Etsy), 10) Measuring sales and engagement. Provide examples and best practices.