In the case of spam, the messages often include unique image URLs that are specific to that message only. The unique URL is used as a tracking ID, so that the image host can identify exactly what message intended for what specific recipient has been viewed, in addition to the date and host accessing the image. This is why many email reading systems do not show images by default, to protect the reader from having their reading of spam being tracked by the email senders.
Domain names serve to identify Internet resources, such as computers, networks, and services, with a text-based label that is easier to memorize than the numerical addresses used in the Internet protocols. A domain name may represent entire collections of such resources or individual instances. Individual Internet host computers use domain names as host identifiers, also called hostnames. The term hostname is also used for the leaf labels in the domain name system, usually without further subordinate domain name space. Hostnames appear as a component in Uniform Resource Locators (URLs) for Internet resources such as web sites (e.g., en.wikipedia.org).
A Content Distribution Network (CDN) is a network of servers distributed geographically. The purpose of a CDN is to deliver content on the internet much faster. If a user in Toronto is trying to access your website, the closest server to them will take care of this. But someone coming to your website from Sydney, Australia, will be catered to by a server closest to them. The main host server holds your website content, and all the other servers have a cached version each.
One option not mentioned in the article is Amazon Photos. Even though I’m an Amazon “prime” customer, I had never really given their photo storage much thought because I already had several sites I use for photo sharing and storage. However, I recently learned that they will store your photos in their original size AND your RAW (CR2, NEF, ARW….) photos too! This is a HUGE advantage for me.
A domain name consists of one or more labels, each of which is formed from the set of ASCII letters, digits, and hyphens (a-z, A-Z, 0-9, -), but not starting or ending with a hyphen. The labels are case-insensitive; for example, 'label' is equivalent to 'Label' or 'LABEL'. In the textual representation of a domain name, the labels are separated by a full stop (period).