It has recently been noticed that ImageShack does a horrible thing: they re-purpose old image URLs for advertising purposes. This can lead the impression that some older posts are actually spam, for example:
But looking closer at the actual content of the post, you can tell that outside the non sequitur image, the post makes sense and is appropriate for the site.
Please do not flag posts containing these images as spam. Spam flags are really meant to identify sources of spam, in particular the user who originally posted. In this case you would be penalising the wrong person.
For examples of what to do, see this meta.MO post by Ilmari Karonen:
... [Try] to recover [the images] from the Wayback Machine by prepending
http://web.archive.org/web/2/to the image URLs, and reupload the recovered images to stack.imgur. (Please don't just leave the image links pointing to archive.org; while this does generally work, we don't really want to rely on them or cause them extra server load.) To make this easier, you may wish to install this user script, which automatically tries to reload ImageShack images from archive.org when you click them, and also highlights such images by graying them out and adding a red dashed border.
If you can't recover the images, and the author of the post is still around, consider leaving them a polite comment to let them know that their post is broken, and asking them to reupload the images if they can. If the author seems to be long gone, see if you can simply edit out the broken images without unduly damaging the post, or perhaps even try to recreate them yourself.
Finally, if the post really seems unrecoverable and useless without the images, you may wish to flag* it or, if you can, just vote to delete it yourself.
*The flag mentioned here should be a "low quality" flag, if possible. Otherwise passing a note to the Reopen? Undelete? Close? Delete? chat room would be a secondary option. Lastly (and likely leastly) a mod-only "other" flag is also a possibility.