urlimage-width-height.go

package main

import (
    "fmt"
    "image"
    _ "image/jpeg"
    _ "image/png"
    "log"
    "net/http"
)

func main() {
    response, err := http.Get("https://golang.org/doc/gopher/doc.png")
    if err != nil {
        panic(err)
    }
    defer response.Body.Close()

    conf, _, err := image.DecodeConfig(response.Body)
    if err != nil {
        log.Fatal(err)
    }
    fmt.Printf("Width=%d, Height=%d\n", conf.Width, conf.Height)
}