Bloom filter wouldn't work. The bloom filter will tell you that a particular URL is "possibly" in the list. What do you do then? Reject it because it might be a tracking image?

[edit] Also, this ignores being able to:

  <iframe src="any-old-tracking-url"></iframe>
  <script src="any-old-tracking-url">
  <link rel="stylesheet" type="text/css" href="any-old-tracking-url">
  <img src="100px-width-tracking-image">

etc