How do you know if you need to seek permission to use something (i.e. a copyrighted image or slogan)

Here is a list of reasons why you would need to seek permission from the original owner:

If you intend to use the material for commercial purposes, you must seek permission from the original owner if that material is copyrighted or is a registered trademark

Or if you want to use the material repeatedly- for example if you are writing a book and you want to include a specific image several times, once again you need to seek the permission to use it from it's original owner

Trademark...What is it?

Nowadays we regularly see the letters "TM" in text, but what does TM (Trademark) actually mean? A trademark is something that a company/business creates for their products or things associated with their company or products. Trademarking their product means that no other businesses have the right to copy the name/design of their trademark and, if they do the company with the official product have the right to take the other company to court. Some common examples of Trademark being used are with Coke or Diet Coke, these are both products created and owned by the Coca-Cola Company and, because they are Trademarked, the names cannot be copied. Companies can also trademark things such as logos or slogans, for example the Nike tick, or swoosh, is trademarked by Nike meaning that no other companies can copy that logo.
The TM logo isn't actually used that frequently, we normally see the letter R encased in a circle (see below) which means that the product or logo's trademark has been officially registered.