Does this seem about right to anyone who happens to know it? It seems right to me from creating pictures on Wabbit and comparing bytes.
Sizes:
Offset Length Description
Packet
| Header
| | 0 11 Standard .8x* header ("**TI83F*" + 1A, 0A, 00)
| | 11 42 Comment (null terminated)
| | 53 2 Data length
| End Header
| Data
| | 55 2 Some kind of header length? (Favor $0D)
| | 57 n Some kind of header*
| | 57+n 2 Always 758 ($02F6)
| | 59+n 2 Always 756 ($02F4)
| | 61+n 756 Picture data (1 bit per pixel, L=>R, T=>B)
| End Data
| 817+n 2 Checksum
End Packet
* Appears to follow this pattern:
F6 02 07 60 ## 00 ...
Where ## is the picture number - 1 as $00 - $FE (possibly FF?)
and ... is null termination to fill the length specified before
EDIT: Nevermind. Apparently it is ^^