Why is GPT-4o unable to access my SAS blob URL from a private Azure Storage account?

When you pass an image URL to the GPT-4o model, the service attempts to fetch the image via a public network call. However, your storage account is secured behind a private endpoint, which means even with a valid SAS token the image isn’t accessible over the public internet. This results in the 403 (Forbidden) error.

There are two common solutions:

1. Use a Publicly Accessible URL:
   Host the image in a storage account (or other service) that is accessible publicly. If you can’t disable the firewall restrictions on your current storage account, consider duplicating the image to a public container or using an intermediary proxy with proper security controls.

2. Pass a Base64 Encoded Image:
   If making the image publicly accessible is not an option, converting the image to its Base64 representation is a viable alternative. As you noted, Base64 encoding works with your code. This bypasses the need for the GPT-4o service to fetch the image via a URL, as the image data is directly supplied in the request.

Here’s a brief example of how you might convert an image to Base64 and use it in your payload:

PYTHONCopied
import base64

# Read the image and convert to Base64
with open("path_to_your_image.png", "rb") as image_file:
    base64_image = base64.b64encode(image_file.read()).decode('utf-8')

# Prepare the messages payload
messages = [
    {
        "role": "user",
        "content": [
            {
                "type": "text",
                "text": "Merge this OCR and previous chat OCR"
            },
            {
                "type": "image_base64",
                "image_base64": {
                    "data": base64_image
                }
            }
        ]
    }
]

completion_json = client.chat.completions.create(
    model=deployment,
    response_format={"type": "json_object"},
    messages=messages,
    max_tokens=800,
    temperature=0.7,
    top_p=0.95,
    frequency_penalty=0,
    presence_penalty=0,
    stop=None,
    stream=False
)

Choose the approach that best fits your scenario:

• If you must use URLs, ensure the image is hosted in an environment that allows public access.
• If you cannot change the network configuration, passing the image as Base64 is the recommended method.

This way, you ensure that the GPT-4o model can successfully process the image without encountering network restrictions.