JPEG: Variation of file-format where EOI marker found more than once

As I understand it, you can figure-out where the follow-up EOI marker is after the scan-data by seeking through it and skipping FFD0 to FFD7 and any FFFF's (escaped/compressed FF), and then just stopping when you hit another marker (which should always be an EOI (FFD9)?).

However, I ran into the following:

003f24d0  ce 51 1b 12 f9 fb a4 1f  bb 40 8f ff d9 00 a8 eb  |.Q.......@......|
003f24e0  2a 83 a7 2a                                       |*..*|

There is an FFD9 but this isn't at the end of the file, nor is it preceded by FF (so it's definitely not an FF byte that was compressed/escaped), nor is it followed by another marker (00 rather than FF) so this isn't some [obvious] mistake.

The file actually ends with an FFD9 (as expected), but when I truncate the file to just after the first FFD9, the image still opens and looks normal. Does anyone know the file-format that I'm dealing with? It seems like there are multiple EOI's separated by undefined data (as far as JPEG goes).

What I find interesting is that I have two images from the same camera that seem to be identical (aside from scan-data), but yet only one has this extra data.

Looks good:

$ file "IMG_6694.JPG" 
IMG_6694.JPG: JPEG image data, Exif standard: [TIFF image data, little-endian, direntries=11, description=                               , manufacturer=Canon, model=Canon PowerShot SX720 HS, orientation=upper-left, xresolution=210, yresolution=218, resolutionunit=2, datetime=2016:09:24 07:32:29, GPS-Data], baseline, precision 8, 5184x2912, frames 3

$ ./js_dump -f "IMG_6694.JPG" 
0x00000002 0xd8 [SOI]
0x00007002 0xe1 [APP1]
0x00007fa0 0xe1 [APP1]
0x00008002 0xe2 [APP2]
0x00008088 0xdb [DQT]
0x0000809b 0xc0 [SOF0]
0x0000823f 0xc4 [DHT]
0x00008241 0xda [SOS]
0x0032d9bb 0x00 [!SCANDATA]
0x0032d9bd 0xd9 [EOI]

Has the extra EOIs:

$ file "IMG_6691.JPG" 
IMG_6691.JPG: JPEG image data, Exif standard: [TIFF image data, little-endian, direntries=11, description=                               , manufacturer=Canon, model=Canon PowerShot SX720 HS, orientation=upper-left, xresolution=210, yresolution=218, resolutionunit=2, datetime=2016:09:24 06:33:29, GPS-Data], baseline, precision 8, 5184x2912, frames 3

$ ./js_dump -f "IMG_6691.JPG" 
0x00000002 0xd8 [SOI]
0x00007002 0xe1 [APP1]
0x00007fa0 0xe1 [APP1]
0x00008002 0xe2 [APP2]
0x00008088 0xdb [DQT]
0x0000809b 0xc0 [SOF0]
0x0000823f 0xc4 [DHT]
0x00008241 0xda [SOS]
0x003f24db 0x00 [!SCANDATA]
0x003f24dd 0xd9 [EOI]
panic: not on new segment marker: (00)

goroutine 1 [running]:
github.com/dsoprea/go-logging.PanicIf(0x5e6900, 0xc4200a2280)
    /home/dustin/development/gopath/src/github.com/dsoprea/go-logging/log.go:476 +0x88
main.main()
    /home/dustin/development/gopath/src/github.com/dsoprea/go-jpeg-image-structure/tools/js_dump/main.go:73 +0x177

The error is due to the file-pointer not sitting at the end of the file but yet not on a new marker.