attachment_image

Most images in Odoo live in binary fields on the record itself. attachment_image covers the other pattern: the record merely points at an existing attachment through a many2one, and the widget renders that attachment as a picture.

The whole component is one template. If the many2one holds a value, it emits an <img> whose source is /web/image/<attachment id>/300x300?unique=1, which asks the server for a version of the attachment scaled to fit inside 300x300 pixels. If the field is empty, the widget renders an empty container and nothing else. There is no upload button, no dialog, no zoom: the source declares supportedTypes: ["many2one"], no options, and no behavior beyond the template.

Its one core job is the kanban cover image. project.task.displayed_image_id is a many2one to ir.attachment restricted to images attached to the task, and the Project, project sharing and To-do kanban cards all render it with this widget.

Cover images are the difference between a kanban board that reads like a spreadsheet and one your team can scan at a glance. A creative agency drops the approved visual on each task card; a property manager shows the unit photo on each maintenance ticket; a manufacturer shows the defect photo on each quality issue. The mechanism is exactly this widget plus a many2one to the record's attachments.

The design has a quiet advantage over binary fields: the image is stored once as an attachment and only referenced by the card, so choosing a different cover never duplicates the file. It also means the picture must already exist as an attachment on the record before it can be shown, which is why the Set Cover Image action in Project opens the task's attachments rather than a file picker.

The core pattern: task cover image

<!-- inside a kanban card template -->
<field t-if="record.displayed_image_id.value"
       name="displayed_image_id"
       widget="attachment_image"/>

This is verbatim how Project renders covers. The t-if guard skips the element entirely for tasks without a cover, which keeps the card compact.

A custom cover field on your own model

<field name="cover_attachment_id" widget="attachment_image"/>

Where cover_attachment_id is a many2one to ir.attachment, typically with a domain limiting it to image attachments of the current record, mirroring displayed_image_id on project.task.

The URL the template builds explains most surprises. /web/image/<id>/300x300 is the generic attachment image route with a resize instruction: the server scales the image down to fit inside the box while keeping proportions, and never scales up. The ?unique=1 suffix is a fixed cache-busting marker, so swapping the cover shows the new picture without a hard refresh.

Because the route resolves the id as an ir.attachment, pointing the many2one at any other model renders broken images, and a user who cannot read the attachment gets the placeholder the route serves for inaccessible records. The tooltip is deliberately quiet: t-att-title is gated on env.debug, so file names only appear when developer mode is on, a small detail added in 17 along with the 300x300 resize. In Odoo 16 the template requested the attachment at full size and always showed the tooltip; 17 tightened both, and nothing has changed since.

Odoo 20 is expected at Odoo Experience in Brussels, 24 to 26 September 2026. We read this widget's file on the public development branch at the time of writing, with the usual caveat that the branch is unstable and anything can still change before release.

No functional changes: the template still renders the same 300x300 attachment URL with the debug-only tooltip. The only movement is the migration to the new Owl props syntax, which affects JavaScript patches, not XML. We re-verify this page once Odoo 20 ships.