^ Background image cover
The div above has a background image that fills the div no matter how it is responsively sized or stretched.
Fluid image
You will use this most of the time!
<img src="..." class="img-fluid" ...Full-width images should be cropped and sized to 2000px wide.
Thumbnail image
Thumbnails will also scale up to max cropped size, and they get a white border and light outline.
Round image
Photo must be cropped square (same height and width), and you add a custom ".rounded-div" class which rounds the img corners.
SVG logo
Copy vector outline from Illustrator and paste into a div, then change the svg's "width" and "height" properties to 100%.