Please provide a link to a page on your site where we can see this. Thanks. Note: Your link will be public and we will not later remove it.
It may be that you’ve been hacked, but it would be interesting to see one of those images.
If you’re unable to clean your site(s) successfully, there are reputable organizations that can clean your sites for you. Sucuri and Wordfence are a couple.
Grab a cup of coffee and take a deep breath. It sounds like you have malware on your site.
There are a number of external scanners, but there are also plugins that you can use.
You can find some in the plugin directory here: https://wordpress.org/plugins/search/malware/
Just remember that cleaning up the symptom doesn’t protect your system. You need to find out how the malware is getting there (for example, if you have a plugin that may be exploitable).
If you do not feel comfortable doing this yourself, you may want to consider hiring someone to do malware cleanup. WordFence and Sucuri are popular recommendations, but I personally admire The Ninja Technologies Network’s work on NinjaFirewall (WP Edition), so I’d add NinTech to that list. 🙂
Hey, thank you for your replies and i m almost too embarrassed to admit it but yea, it was completely my mistake there as i had forgotten there was a plugin downloaded (Magic Post Thumbnail) that did exactly this….So simple solution this time! And sorry for the bother!