Is there value in optimizing stock images on site?

[chrisvogel]

We have a whole bunch of websites that all use stock imagery. Some of the images have alt tags on them but some of them do not. To add alt tags to all of them would be a pretty lengthy process. So, would there actually be any value in adding these tags to stock images across the board?

[Mobilio]

CDN isn't pure fun for SEO because you give links to other companies or domains.

I can do http://cdn.example.com/ or http://examplecom.amazoncdn.com/ as closest example - then your both links to images goes away and isn't too good.

Only way is if your site and images are on same domain/subdomain. But this require very good planning of deploying. And in result you will be "vendor locked" for cloud solution.

[TimHolmes]

Maybe also serve them from a CDN (Content delivery network) for added speed and performance gains to go with your Alt tag edits.

[TimHolmes]

As a side note, I would also look to make sure all images have been compressed via something like lossless compression to reduce their file size and hence speed up your site for another boost.

A cool online free tool I use is compressor.io. In general the quality remains, but you can often reduce filesize by anything up to 50%.

Again this might be lengthy but should help users when visiting your site etc.

[Mobilio]

Yes, there is!

https://moz.com/search-ranking-factors/survey
https://moz.com/blog/is-optimizing-photos-more-important-than-you-think
https://moz.com/learn/seo/on-page-factors
https://www.shopify.com/blog/7412852-10-must-know-image-optimization-tips
https://yoast.com/image-seo/
http://www.koozai.com/blog/content-marketing-seo/increase-traffic-with-images/

That's why you MUST include ALT attribute to each image that you didn't use for design purposes in HTML.

[ChrisAshton]

Absolutely. Unique or stock, all images should be treated exactly the same way