faster fopen or file_get_contents?

Question

i am running multiple websites with high traffic , as a requirement , all images are downloaded via image.php?id=IMAGE_ID_HERE . If you ever done that before , you know that that file will be reading the file image and echoing it to the browser with special headers .

My problem is , the load on the server is very high (150-200) and TOP command shows multiple instances of image.php , so image.php is running slow !

the problem probably is fopen loading the image to the memory before sending it to the client. How to read a file and pass it through directly?

Thank you guys

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UPDATE

After you optimized the code, used caching wherever possible, do create a CDN . couple of servers, sync methods, load balancers and no need to worry about requests anymore :)