We're working with a site that has gone through a lot of changes over the years - ownership, complete site redesigns, different platforms, etc. - and we are finding that there are both a lot of pages and individual images that are returning 404 error codes in the Moz crawls. We're doing 301 redirects for the pages, but what would the best course of action be for the images? The images obviously don't exist on the site anymore and are therefore returning the 404 error codes. Should we do a 301 redirect to another similar image that is on the site now or redirect the images to an actual page? Or is there another solution that I'm not considering (besides doing nothing)? We'll go through the site to make sure that there aren't any pages within the site that are still linking to those images, which is probably where the 404 errors are coming from. Based on feedback below it sounds like once we do that, leaving them alone is a good option.

I've been doing SEO for a little over 4 years. I've never used sites like Digg, Stumbleupon, Reddit, etc. either personally or on behalf of my clients. This past week I had a discussion with another SEO who asked what I'm doing for my clients with regard to social bookmarking. I responded that I'm really not doing anything and they were shocked. I took a pretty good verbal beating over it. She was borderline offended. I have always been able to deliver solid results for my clients without any type of social bookmarking, so I struggle to see the need, but am surprised at how shocked this other SEO was that I don't do it. How beneficial is it and am I really missing out?