How to Set a Default Image for a Binary Field in Odoo (16–19)

my_module/
├── __manifest__.py
├── __init__.py
├── models/
│   └── my_model.py
├── static/
│   └── img/
│       └── default_avatar.png   ← default image file goes here

# models/my_model.py
import base64
from odoo import fields, models
from odoo.modules.module import get_module_resource


def _default_image():
    """Read the bundled default avatar and return it as base64 bytes."""
    img_path = get_module_resource("my_module", "static", "img", "default_avatar.png")
    with open(img_path, "rb") as f:
        return base64.b64encode(f.read())


class MyModel(models.Model):
    _name = "my.model"
    _description = "My Model"

    name = fields.Char(required=True)

    image_1920 = fields.Image(
        string="Image",
        max_width=1920,
        max_height=1920,
        default=_default_image,   # ← pass the function object, not the call
    )
    # Odoo auto-generates image_128 and image_256 shadow fields from image_1920

# models/my_model.py  (Odoo 12/13 legacy pattern)
import base64
from odoo import fields, models
from odoo.modules.module import get_module_resource


def _default_image():
    img_path = get_module_resource("my_module", "static", "img", "default_avatar.png")
    with open(img_path, "rb") as f:
        return base64.b64encode(f.read())


class MyModel(models.Model):
    _name = "my.model"
    _description = "My Model"

    name = fields.Char(required=True)

    image = fields.Binary(
        string="Image",
        attachment=True,   # store in ir.attachment instead of database column
        default=_default_image,
    )
    image_medium = fields.Binary(
        string="Medium Image",
        attachment=True,
    )
    image_small = fields.Binary(
        string="Small Image",
        attachment=True,
    )
    # In legacy Odoo 12/13, you had to generate resized variants yourself.
    # In Odoo 14+ with fields.Image, this is automatic.

# Alternative using file_open
import base64
from odoo import fields, models
from odoo.tools.misc import file_open


def _default_image():
    # file_open path: <module_name>/<relative_path_within_module>
    with file_open("my_module/static/img/default_avatar.png", "rb") as f:
        return base64.b64encode(f.read())


class MyModel(models.Model):
    _name = "my.model"
    _description = "My Model"

    image_1920 = fields.Image(
        string="Image",
        max_width=1920,
        max_height=1920,
        default=_default_image,
    )

<!-- views/my_model_views.xml -->
<record id="view_my_model_form" model="ir.ui.view">
    <field name="name">my.model.form</field>
    <field name="model">my.model</field>
    <field name="arch" type="xml">
        <form string="My Model">
            <sheet>
                <field name="image_1920"
                       widget="image"
                       class="oe_avatar"
                       placeholder="/my_module/static/img/default_avatar.png"/>
                <group>
                    <field name="name"/>
                </group>
            </sheet>
        </form>
    </field>
</record>

# __manifest__.py
{
    "name": "My Module",
    "version": "17.0.1.1.0",
    "post_init_hook": "post_init_hook",   # ← add this
    ...
}

# __init__.py
from .hooks import post_init_hook   # ← add this

# hooks.py  (new file)
import base64
from odoo.modules.module import get_module_resource


def post_init_hook(env):
    """Back-fill default image on records that have none."""
    img_path = get_module_resource("my_module", "static", "img", "default_avatar.png")
    with open(img_path, "rb") as f:
        default_image = base64.b64encode(f.read())

    records_without_image = env["my.model"].search([("image_1920", "=", False)])
    records_without_image.write({"image_1920": default_image})