How do Zotero PDF metadata and Crossref queries turn a screenshot into a locatable record?

If your screenshot is actually a PDF, run Zotero's Retrieve PDF Metadata first; if you only have an image, transcribe the title and author and query Crossref instead. The two routes need different inputs, so the file format decides which one you can use.

Route 1: You have the PDF

1. Add the PDF to Zotero as a standalone file. Zotero can attempt to create a parent bibliographic item for a standalone PDF by using identifiers or extracted metadata.
2. Run Retrieve PDF Metadata on that item. The expected result is a parent item built from whatever identifiers or metadata Zotero could extract.
3. Open the new record and check each field against the first page in your screenshot. Correct any field that does not match. The record is only as good as this check.
4. If the record now carries a DOI, use it as your stable identifier. A DOI name resolves through the Handle System to current information supplied for the identified object, commonly a landing page maintained by the registrant.

Route 2: You only have an image

1. Transcribe the title and author exactly as printed, including any subtitle.
2. Query Crossref with those bibliographic terms. Crossref documents bibliographic queries, filters, result selection, cursor paging, and polite API use for retrieving and narrowing scholarly metadata.
3. Compare the returned candidates against your screenshot. Use filters and result selection to narrow the list when the title is common.
4. Take the DOI from the candidate that matches your transcription, then resolve it to confirm it points to the paper you have.

Which route yields a DOI or stable identifier?

Both routes can end in a DOI, but they get there differently. Zotero's retrieval works from identifiers or metadata inside the PDF, so a PDF with embedded identifiers gives it more to work with. A Crossref query works from the text you transcribe, so its result depends on how completely and accurately you copy the title and author. If the PDF route produces a record without a DOI, or the Crossref results do not clearly match your transcription, treat the record as unresolved and verify the candidate against the printed page before citing it.

For a deadline, start with whichever input you actually have, then spend your remaining time on the field check rather than on a second lookup.