Hi, From what I've read, I could see that site-wide links are not to Google's liking. I could imagine that it is the case for the text links. I was looking at one of my sites today and I saw that I had a banner ad in all pages of that site to another site of mine. And then I linked this with the speculation about site-wide links. So, an image link like in this case would also be considered a site-wide link and get penalized? Thanks in advance.
You wouldn't get a penalty, google would just ignore it. If your sites are with the same host, they are likely already ignoring it.
Are you referring to all site-wide links (text links - image links) or just the image links in this case?
If a link shares the same class "c" IP, google assumes common ownership. Owners "voting" (linking) to their own sites are not natural links, so google ignores them. Site wide links do not look as natural as a link inside of relevant text - so regardless of the ip address, google is going to discount or ignore it whether or not it is a text or image link. A text link certainly carry more weight than an image link.