I have a site where people can upload pictures to a submission that gets posted onto my homepage. With that, obviously, the images show up on my homepage. Is there anything I can do to optimize those images or implement SEO onto them, like adding my keyword as an alternate text or something?
Alt text and title text would be fine, Getting your users/posters to enter alt text as a descriptive aspect of the image will help a little. Or if you are running your own CMS maybe get it coded so that images have a mandatory field to "add a description"
Yes , Although it would save you alot of work if your posters done it them selves etc . If you are happy to add them all then go for it , It definitely wont do you any harm and has the "potential" to help your sites natural search , Obviously dont expect to see massive results changes because it wont be the case , Likely hood is that google will take some time to re-crawl those older pages etc , which is another reason to get your posters to input the Alt text when posting the image , because then the first crawl that hits the page will see the relevant alt text , where if you add it at a later date it could be week's before it gets crawled again etc.
I think it would save you a lot of time to have the posters insert their own alt text -- If you end up with an active site that attracts hundreds of posters, you would quickly be overwhelmed trying to add alt text to each new image yourself.
Well I can add the description and stuff before it gets posted. When their submission gets sent to me for approval, I can go into the images they attached to their submission and insert my own alternative text and stuff to the images if I want.