Being a computer file, a JPEG file is made of multiple bytes. One byte in hexadecimal could look like 0x01. The very first bytes of a JPEG are 0xFF, 0xD8 ("FF D8"); these bytes are named Start Of Image (SOI). The first section of bytes in a JPEG is the header; this is from FF D8 to right before the last 0xFF, 0xDA ("FF DA") bytes. The header contains data about the data and other helpful data. The next section of bytes in a JPEG is the image data; this is from FF DA to 0xFF, 0xD9 ("FF D9"). The FF DA bytes are named Start Of Scan (SOS), and the FF D9 bytes are named End Of Image (EOI).