What is Base64?

Base64 takes three bytes of input (24 bits) and encodes them as four 6-bit characters from the alphabet A-Z a-z 0-9 + / (with = for padding). The output is roughly 33% larger than the input, but it is pure ASCII, so it survives any text channel: JSON, XML, email bodies, URLs (with the URL-safe variant), HTTP headers.

Common uses: embedding small images directly in CSS or HTML as data:image/png;base64,... URIs, sending binary blobs in JSON APIs, encoding credentials in Authorization: Basic headers, encoding JWT payloads. Despite frequent misuse, base64 is not encryption; anyone who reads the string can decode it back to the original bytes.

For brand and crawling work, base64 shows up most often as inline images or fonts in HTML and CSS. A favicon is sometimes a data: URI. Logos are sometimes inlined to avoid an extra HTTP round trip. Decoding those is one line of code in any language and recovers the underlying PNG, SVG, or WOFF.