A browser’s network panel shows 304 where you expected 200. The page may still load normally because the response participates in checking a copy already stored by the client.
Read the request alongside the response
MDN describes 304 Not Modified as a response to a conditional request indicating that retransmission of the resource is unnecessary. It does not carry a new response body. Looking only at the body size therefore misses the role of the cached representation.
Keep the conclusion narrow
A 304 for one image does not certify that every part of a page is current or working. Inspect the particular resource and its request conditions. Scripts, styles and the main document may follow different cache paths.
For a troubleshooting note, save the resource URL, method, status and relevant cache headers after removing private information. Describe the visible problem separately. This gives a developer evidence to examine without replacing the actual symptom with the mistaken claim that a 304 is automatically an error.