Currently, photos and images are not crawlable. What that means is this: Search engines will never index images on the basis of the images alone. In order to get your photos indexed in the search engines you’ll have to include alt tags for them. An alt tag is a text equivalent of a photo that tells search engine crawlers what the photo is about. But what about duplicate photo content?
You know that if you have two websites with similar content then at least one of them will show up as duplicate content and you’ll get a penalty. Will that happen with photos as well?
Answer: It will if your alt tags are the same. Therefore, if you want to by pass the duplicate content penalty for photos and images, you’ll need to alter your alt tags for each image even if the images themselves are the same.
Here’s an example: Let’s say you have a photo of Knute Rockne after winning his last football game at Notre Dame. It is an action shot of the team hoisting Rockne high on their shoulders and carrying him off the field (I don’t know if that really happened). Rockne’s winning smile and his right hand holding a football high above his head makes the photo a great shot.
Now let’s say you put that photo on one website then publish it on another website two weeks later. Same exact photo, no modifications. On the first publication your alt tag reads “knute rockne wins.” On the second publication of that photo you make your alt tags “coach knute rockne on his last game at notre dame.” Chances are, these two photos will not appear as duplicate content in any of the search engines because the search engine crawlers are reading the alt text, not the photo images themselves.
On the other hand, let’s say that you have a photo of Knute Rockne’s first game at Notre Dame and publish that on the second website right next to the duplicate photo you published at Website 1. Now, give it the same alt tag that you gave Photo #1 on Site #1: “knute rockne wins.” Duplicate alt tag, but does that translate into duplicate content? I’m pretty sure it will because the search engines are looking at the alt tag and know that it describes a photo. Even though they can’t crawl each individual photo to determine whether they are the same or not, they make judgments based on your alt tags.
Here’s your lesson: Never use the same alt tag twice.