Trackers without width or height properties defined in the <img /> element

[oneofthedamons]

I emailed you a sample of one of these:

<IMG alt="" hspace="0" border="0" src="https://example.org/smtp.mailopen?id=21835077" />

(I redacted the domain with example.org)

Pretty sure it's a tracker as it has what appears to be a unique identifier and returns a GIF image 1 px x 1 px. However, neither the width nor height properties of the <img /> element are defined.

Is this a way for trackers to get around the heuristic for identifying them?

[apparition47]

Yep. These ones are a bit trickier.

I spotted a similar link in this mail of this mailing list. The thing these sites have in common is that they're run on this site called Blackbaud. So going to list it under there for now.

Thanks!