title: Adding files that rely on pipeline outputs
body: <p>In my workflow, I do the following:</p>
  <ol>
  <li>Acquire raw data (e.g. a video containing people)</li>
  <li>Transform it (e.g. automatically extract all crops with faces)</li>
  <li>Manually label them (e.g. identify the person in each crop). The labels are stored in json files along with the crops.</li>
  <li>Train a model on these data.</li>
  </ol>
  <p><strong>How should I track this pipeline with DVC?</strong></p>
  <p>My concerns:</p>
  <ol>
  <li>If stage 2 is changed (e.g. crops are extracted with a different size), the manual data should be invalidated (and so should the final model).</li>
  <li>The 3rd step is manual and therefore not precisely reproducible. But I do need its input to be reproducible.</li>
  <li>Stage 4 has an element of randomness, so it's not precisely reproducible either.</li>
  </ol>