Pixabay is a free-to-use image bank. All the images are useable under a Creative Commons license and therefore are royalty free and no attribution is required (although you can, if you wish, mention the artist/photographer). The quality is incredible. With over a million images that you can discover it is an amazing graphic resource. It's very user friendly as you can type in a term or word in the search bar at the top and the relevant imagery will come up. This makes it perfect for use in social media or design projects. When you click on an image you can choose the download quality (although the highest level requires you to register as a user). I love the exceptional quality of the images and also sometimes look through these in order to cheer myself up. There are all sorts of media types from watercolour images, to landscape photographs, to digital designs. Graphics are usually jpg format although there are vector pngs too (transparencies) so you can use these to layer your own creations. They also have a video bank too so you can also use these to create projects.
Very few issues - it's a beautiful website full of beautiful images. How they generate income other than through the donation system is via advertising other image services such as Shutterstock. At the top of the screen or below a Pixabay image you may end up accidentally clicking on Shutterstock which is not royalty free and does require payment (so use caution to check you are still on Pixabay).
Also you need to be aware of using images that may contain identifiable people or products. For example, some of the artists may take a photograph that could include a Disney character so with this you need to ensure you do not use these whereby it could be taken that Disney is somehow endorsing your products or services. Although Pixabay run some checks you still need to be aware of how copyright laws work.
Anyone in any industry - it's easy to find and search for images to use for social media or projects or blogs. For health coaches there are perfect graphics for using in marketing materials including food imagery. There are even graphics you could use to inspire a client who maybe wants to create a vision board. Beaches, balloons, bubbles, chocolate, canoes, mountains, goats - anything you want is on Pixabay as a graphic.
I would suggest playing with search terms to find the perfect image you want.