Start by naming the transport
An SSDV receive session is only partly an image problem. First identify how the bytes are supposed to arrive: RTTY, AX.25 over AFSK, a KISS TCP stream, a 9600 packet downlink, or a mission-specific frame layer. The same SSDV packet can be perfectly valid while the radio layer around it is completely different.
Record raw audio or IQ when possible. A weak first decode is still useful if you can replay the channel, adjust demodulator settings, and export the recovered packet stream. Once packet bytes are preserved, multiple listeners can often contribute different missing pieces of the same image.
Keep the image key visible
The practical image key is callsign plus image ID. Packet ID then orders the fragments. When a ground station receives interleaved images or retransmissions, grouping by those fields prevents a decoder from joining good packets into the wrong JPEG.
Log packet health, not just final image health
Before decode
Frequency, transport, baud or symbol rate, demodulator, UTC start, receiver, antenna, and audio or IQ sample rate.
During packet recovery
Valid packets, CRC failures, FEC corrections, missing packet IDs, callsign, image ID, and whether EOI was seen.
After reconstruction
JPEG completion state, visible gaps, duplicated packets, merged listener sources, and whether the raw packet file was archived.
When the picture is broken
A broken SSDV image does not always mean the picture content was weak. It can mean the modem slipped by one byte, a packet boundary was missed, Reed-Solomon could not correct the remaining byte errors, packet IDs arrived out of order, or the decoder needed the MCU offset to skip the tail of a lost block. Diagnose from the packet log before judging the RF path.