WhatsApp image message: JPEG or PNG, 5 MB, 1024-character caption

An image message on the WhatsApp Cloud API accepts JPEG or PNG only, 8-bit RGB or RGBA, up to 5 MB, with a caption of at most 1024 characters. Meta recommends sending by uploaded media id instead of a link. Sume Images can output both formats; check the byte size before you upload.

What are the image rules?

They come from Meta's image message page and its media reference. A request with an invalid or expired media id, or an unsupported image type, returns an error response instead of a message id.

How do I make a compliant file?

Request jpeg for photos and png for flat graphics. WebP is not accepted for image messages, though it is for stickers, so avoid webp here. A 1:1 or 4:5 ratio reads well in chat; Meta states no ratio rule in the pages read.

import json, os, urllib.request

body = {
    "model": "bytedance-seed/seedream-4.5",
    "prompt": "product photo of a canvas tote on a plain backdrop",
    "aspect_ratio": "4:5",
    "output_format": "jpeg"
}
req = urllib.request.Request(
    "https://api.sume.com/v1/images",
    data=json.dumps(body).encode(),
    headers={
        "Authorization": "Bearer " + os.environ["SUME_API_KEY"],
        "Content-Type": "application/json",
    },
    method="POST",
)
print(urllib.request.urlopen(req).read().decode())

Which delivery method should I use?

Upload once and send by media id. Meta's media reference says API uploads persist 30 days and media URLs expire after 5 minutes, which the related post covers. A hosted link is possible but not recommended.

What should I verify?

Check Meta's current pages before launch. The images guide covers Sume.