File Types

Images

Captain indexes an image as one record with two signals: a native image embedding computed from the pixels, and a written description stored as searchable text. This page covers what the description contains, when an image is split, what a result contains, masking, and the limits.

This is useful for

  • Screenshots of dashboards and tools, found by the text on the screen
  • Photos from the field, found by a serial number on a plate or by what the photo shows
  • Whiteboards, labels and single-page scans that should be transcribed word for word
  • Scanned forms that need PII painted out before they are indexed

What one image becomes

  • A native image embedding, computed from the pixels. This lets a query such as “a red forklift in a warehouse” match a photo that contains no text.
  • A written description, stored as text on the same record. A vision model transcribes every visible word verbatim (labels, titles, numbers, part codes, watermarks, handwriting), renders tables as markdown, reads charts (axis labels, values, series, trend) and describes the scene.

Formats other than PNG and JPEG are converted before the vision pass. EXIF orientation is applied, so a sideways phone photo is read the right way up. Animated GIFs and multi-page TIFFs use their first frame.

How an image is chunked

1

One record, two signals

The pixels are embedded once, and the description is stored as text beside the embedding. A query matches the image by vector similarity to the pixels, by the words in the description, or both. match_sources on a result says which.

2

Verbatim transcription

The description is written to be searched. Every visible word is transcribed as it appears, so a serial number on a plate or a metric label on a dashboard matches as text. The stored content starts with [Image: file name] followed by the description.

3

Dense tables

When the description contains a table of five rows or more, a layout model re-reads the image into a fixed grid. The table is written out in row sections with the header repeated, and the row count is cross-checked against the first transcription.

4

When an image is split

A photo or a logo is one chunk. A text-heavy image (a full-page scan, a long screenshot) is split into several chunks at its section headings so each passage stays small enough to match precisely.

Query results

An image result has modality: "image", text set to the description, and document.source naming the file. Collections that contain media rerank by default because vector scores from images and text are not on the same scale; see Multimodal Search.

Limits, masking and billing

Images are accepted up to 200 megapixels decoded (about 20,000 x 10,000). The check reads the header first, so a small file that would decode to an enormous raster is refused without being decoded. A corrupt or truncated file fails with an error that names it, and only that file fails. Route size limits are on File Size Limits.

With mask_pii on, OCR finds words that carry PII (and, on ID documents, the field values next to the labels), and solid boxes are painted over them in the copy Captain indexes. Small images are upscaled up to 4x toward a 3,000 px short side before OCR, because small print is missed at native resolution; the long side is capped at 4,000 px. The description is masked as well. If masking fails, the image is not indexed. The original file is not modified.

Billing is 0.5 credits per image.

Examples

Goal: find a screenshot by the numbers on the screen, from a folder of files named Screenshot 2026-03-04.png.

request
{
  "query": "conversion rate by channel, March",
  "limit": 5
}
result (one item)
{
  "modality": "image",
  "match_sources": [
    "keyword",
    "content_embedding"
  ],
  "text": "[Image: Screenshot 2026-03-04.png]\nDashboard titled 'Acquisition, March 2026'. Table: Channel | Sessions | Conversion rate. Paid search | 41,200 | 3.8% ...",
  "document": {
    "id": "…",
    "name": "Screenshot 2026-03-04.png"
  }
}

The on-screen text is transcribed verbatim into the description, so the file name does not matter.

Goal: find a photo by the serial number on its plate, limited to one site.

request
{
  "query": "pump serial PX-4471-B",
  "limit": 3,
  "filter": {
    "site": {
      "$eq": "plant-2"
    }
  }
}

The serial number is in the description as text. Photos without text still match on the image embedding.

Goal: index a one-page scan as one record with a full transcription and a redacted copy. For a multi-page scan that needs page ranges and block-level citations, send it as a PDF instead; see Documents.

index request (form fields)
{
  "mask_pii": true,
  "custom_metadata": {
    "form": "KYC-2"
  }
}

OCR runs on an upscaled copy, boxes are painted into the indexed copy, and the description is masked.

See Supported File Types for the extension table.

© 2026 Captain