Depending on whether the mail client supports it, theoretically you can use a URI scheme for example:
<img src="data:image/png;base64,
iVBORw0KGgoAAAANSUhEUgAAAAoAAAAKCAYAAACNMs+9AAAABGdBTUEAALGP
C/xhBQAAAAlwSFlzAAALEwAACxMBAJqcGAAAAAd0SU1FB9YGARc5KB0XV+IA
AAAddEVYdENvbW1lbnQAQ3JlYXRlZCB3aXRoIFRoZSBHSU1Q72QlbgAAAF1J
REFUGNO9zL0NglAAxPEfdLTs4BZM4DIO4C7OwQg2JoQ9LE1exdlYvBBeZ7jq
ch9//q1uH4TLzw4d6+ErXMMcXuHWxId3KOETnnXXV6MJpcq2MLaI97CER3N0
vr4MkhoXe0rZigAAAABJRU5ErkJggg==" alt="Red dot" />
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URI -:
- Gecko, Firefox, XeroBank, Camino, Fennec K-Meleon
- Konqueror, / KDE KIO
- Opera ( , Nintendo DSi Wii)
- WebKit, Safari ( iPhone), Android, Epiphany Midori (WebKit Konqueror KHTML, Mac OS X KIO, ), Webkit/Chromium, Chrome Iron
- Internet Explorer 8. "" , , , JavaScript, URI , script , - . URI 32 KiB.
, IE8 32 . , , URI IE8. IE7 .