无法从本地Flask服务器加载图片至React应用求助

我在React应用中尝试展示通过POST请求本地Flask服务器获取的图片，试过字节数组和URL两种方式都失败了，Firefox检查器显示“无法加载图片”。

图片本身无问题，可在VS Code中正常查看；未出现内容安全策略（CSP）或跨域资源共享（CORS）错误；直接从仓库加载占位图到img元素可正常显示。运行环境为Windows 10 Enterprise。

尝试1：Flask返回send_file #

Flask POST方法末尾代码：

output.save("path/to/my/outputs/generated.png", "PNG") 
return send_file("path/to/my/outputs/generated.png", mimetype='image/png') 

React fetch函数：

fetch(
    "http://localhost:5000/path", 
    {
        method: "POST",  
        mode: "cors", 
        body: data
    }
)
    .then(response => {
        let reader = new FileReader();
        let blob;
        reader.onload = (event) => {
            blob = new Blob([response as unknown as BlobPart], {type: "image/png"})
            event.target && setSelfie(event.target.result);
            reader.readAsDataURL(blob)
        }
    })

React函数组件代码：

const [selfie, setSelfie] = useState(placeholderImage)

return (
    <>
        ........
     
        <img 
            src={selfie}
            alt={placeholderImage}
            width={768}
            height={768}
        />
    </>
)

结果：img的src为data:image/png:base64,iVBORw0KGgo etc etc，Firefox提示“无法加载图片”。

尝试2：Flask返回Base64编码的JSON响应 #

Flask代码：

with open("path/to/my/outputs/generated.png", "rb") as file:
    saved_img = file.read()
    saved_img_b64 = base64.b64encode(saved_img).decode('utf-8')
    response = {}
    response['data'] = saved_img_b64
    return Response(json.dumps(response))

React响应处理代码：

.then(response => response.json())
.then(json =>{     
    setSelfie(`data:image/png:base64,${json["data"]};`)
})

结果：img的src为data:image/png:base64,iVBORw0KGgoAAAANSUhEUgAAAb etc etc，Firefox仍提示“无法加载图片”。

尝试3：Flask直接返回Base64字符串，React用API路径作为src #

Flask代码：

with open("path/to/my/outputs/generated.png", "rb") as file:
    saved_img = file.read()
    saved_img_b64 = base64.b64encode(saved_img).decode('utf-8')
    return saved_img_b64

React img设置：

<img src="http://localhost:5000/path" width={768} height={768} alt="generated image" />

结果：Firefox提示“无法加载图片”。

内容的提问来源于stack exchange，提问作者cudnn_account