Encodes an uploaded image into a Base64 data URI with the background-image rule and <img> tag that use it, reporting the size overhead; SVG text can be percent-encoded instead of Base64. Paste a data URI to decode it: the real format is sniffed from the file signature (PNG, JPEG, GIF, WebP, AVIF, BMP, ICO, SVG) and compared with the declared type, and the image is rendered in the preview. Everything runs locally.