Drop a TIFF above, get a JPG back that any browser, phone or web form will accept.
TIFF is the format your scanner chose for you. Flatbed scanners, fax gateways, museum archives and medical imaging kit all default to it, because it stores an image without throwing anything away and can hold several pages in one file. It has been doing that job since 1986 and does it well.
The trouble starts when the file leaves the scanner. No browser displays a TIFF. Chrome, Firefox and Edge have never supported it; Safari's handling is partial and depends on the version. Upload forms reject it, phone galleries ignore it, and the person you emailed it to opens their attachment to find nothing happens.
JPG is the opposite trade. It discards detail your eye is least likely to notice, and in exchange it opens on every device made this century at a fraction of the size. A 40MB archival scan routinely lands under 2MB.
Multi-page TIFFs give you the first page here. That is the limit of a tool that promises one image out. If your scan is a document rather than a picture, TIFF to PDF keeps every page and gives you something you can email.
Keeping every pixel instead: TIFF to PNG compresses losslessly, which suits scanned text, line drawings and anything you intend to edit later.
Drop a stack of scans and they come back together as a ZIP.