Is it legal to use ‘royalty-free’ stock images I found online?

Simply being labelled 'royalty-free' or 'free to use' does not automatically mean an image is genuinely free of all restrictions or safe to use in every context, since these terms are often used loosely, and copyright protection under the Copyright Act, Chapter 415 of the Laws of Malta, and similar principles internationally, still generally applies to such images, with the specific license terms attached to a genuinely free image often including conditions, such as requiring attribution, prohibiting commercial use, or restricting certain types of modification, which are easy to overlook if images were gathered casually without carefully reading and recording the actual licence terms for each one. Given that you haven't been tracking exactly where each image came from or under what specific licence terms, you may currently be unable to properly verify whether your use has actually complied with the applicable conditions, which creates a genuine, if currently unquantified, risk of a copyright claim from an actual rights holder if any of these images turn out to have been used outside their permitted terms, or were never genuinely free to use at all despite how they were labelled where you found them. Going forward, it would be sensible to only source images from clearly reputable stock image platforms with verifiable licensing terms, keep proper records of the specific licence for each image used, and consider having a lawyer review your current situation and materials to assess your actual exposure and any practical steps to reduce risk.