Depends on the specific circumstances, the actual licensing of the image. You're always allowed to cite an image on your page via embedding it from the source by its URL, but then you need to add the citation reference to the source, and not abusing "citation" if you're not making statements about the image. If the image is published under the default "all rights reserved" (no license granted or obtained by you, so it's only on their own site available to visitors of their site), the copyright holder might deny commercial use, and if you embed it in your site that has something to do with money (including ads or being part of your business operations), then that could easily be seen by a court as a copyright violation. Furthermore, you may infringe other rights apart from copyright, if you put the image in a context that's misleading or defamatory. Then there's lots of special regulation in many countries and jurisdictions as there is no international copyright law, for example concerning if the hoster/operator is responsible if users post image link embedding like you're describing, or the attempts to make citations/linking illegal if the source is already violating copyright.
Keep in mind that this isn't legal advice, and the law in many cases is totally stupid and outdated and shouldn't play a role in certain respects anyway.