diff --git a/codec/mjpeg/jpeg.go b/codec/mjpeg/jpeg.go
index 52d68418..77b8a6ec 100644
--- a/codec/mjpeg/jpeg.go
+++ b/codec/mjpeg/jpeg.go
@@ -52,6 +52,25 @@ const (
 	codeEOI  = 0xd9 // End of image.
 )
 
+// Density units.
+const (
+	unitNone = iota
+	unitPxIN
+	unitPxCM
+)
+
+// JFIF header fields.
+const (
+	jfifLabel       = "JFIF\000"
+	jfifVer         = 0x0201
+	jfifDensityUnit = unitNone // Units for pixel density fields.
+	jfifXDensity    = 1        // Horizontal pixel desnity.
+	jfifYDensity    = 1        // Vertical pixel density.
+	jfifXThumbCnt   = 0        // Horizontal pixel count of embedded thumbnail.
+	jfifYThumbCnt   = 0        // Vertical pixel count of embedded thumbnail.
+	jfifHeadLen     = 16       // Length of JFIF header segment excluding APP0 marker.
+)
+
 var (
 	errNoQTable  = errors.New("no quantization table")
 	errReservedQ = errors.New("q value is reserved")
@@ -262,15 +281,14 @@ func writeHeader(p *putBuffer, _type, width, height, nbqTab, dri int, qtable []b
 
 	// Write JFIF header.
 	mark(p, codeAPP0)
-	p.put16(16)
-	const jfifLabel = "JFIF\000"
+	p.put16(jfifHeadLen)
 	p.putBytes([]byte(jfifLabel))
-	p.put16(0x0201)
-	p.put8(0)
-	p.put16(1)
-	p.put16(1)
-	p.put8(0)
-	p.put8(0)
+	p.put16(jfifVer)
+	p.put8(jfifDensityUnit)
+	p.put16(jfifXDensity)
+	p.put16(jfifYDensity)
+	p.put8(jfifXThumbCnt)
+	p.put8(jfifYThumbCnt)
 
 	// If we want to define restart interval then write that.
 	if dri != 0 {