You can use any of the popular image hosts and either https://archive.org/web/ or https://archive.is/, the latter seems to be more popular.
There are also several image hosts available, including /v/veuwer, which was made specifically for voat (and why I mention it here) and is free of agenda. However, images are static and not interactive, so while they are OK to use if you find it more convenient, it's recommended you archive the page instead.
Edit: Since there are typically several posts on this topic every time this isn't stickied, I've decided to have it as a default sticky unless there's either something take precedent or we decide that directly linking to reddit should be against the rules. I'll likely be editing the post text to keep it relevant, so I've archived the original post here.