What are 'src' and 'srcset'?
The 'src' attribute determines the source of an image element, such as a path in folders to a specific image file.
The 'srcset' attribute allows the browser to choose an image from a selection of sources, and the size of each image.
Size Attribute
The 'sizes' attribute will allow the browser the ability to choose an image size based on the current size of the browser window. 'Sizes' acts as a list that uses conditions to set an image size, and only one condition can be met at a time. If no conditions are met, the image will either use the bottom width provided that has zero condition next to it, or the default image width if a non-condition width isn't provided.
What is Art Direction & Why is it Used?
Art direction, in respect to web design, focuses on improving the visual style and design of a website to relay a specific message or emotion. This is primarily done through proper UI and UX design, where UI focuses on visuals design, while UX focuses on the emotions felt when using a website.
The purpose of using art direction is for users to have the best experience while visiting your site, encouraging future visits. There are several ways art direction can be used to better a user's experience, those being consistent design, visual storytelling, balanced aesthetics and functionality, unique identity, and staying up-to-date on trends.
Consistent design allows users to get the basic structure of your website down, and allows them to know where to expect similar content. Visual storytelling can focus on the way you are presenting your content; if it's serious, go simple and choose neutral colors that work well, and if it's playful, choose brighter colors. Finding a balance between, "this looks really cool, but is hard to use" and "I can use it easily, it just looks bland" will make the browsing experience more fun to user's on your site. Having a unique identity makes you stand out from other websites, and is more likely to be remembered than a look-a-like. Lastly, staying up to date on website content and even integrating newer features into your site can greatly change how users feel when on your site.
Summary
All to say, art direction is a concept that focuses on making a user feel a certain way, or communicate some sort of message to them, and there are plenty of ways to modify a website to convey different emotions or messages. In addition, the 'src' attribute is the standard image source attribute, but 'srcset' and 'sizes' can allow images to become much more responsive while browsing a site on varied devices.