snapshot_filename 
 
-  Type: String
  -  Range / Valid values: Max 4095 characters
  -  Default: %v-%Y%m%d%H%M%S-snapshot
  -  Group: Output - Picture
 
 
File path for snapshots (jpeg or ppm) relative to target_dir., File path for snapshots (jpeg or ppm) relative to target_dir.
Default value is equivalent to legacy 'oldlayout' option. For Motion 3.0 compatible mode (directories based on date and time) choose: %Y/%m/%d/%H/%M/%S-snapshot
File extension .jpg or .ppm is automatically added so do not include this
A symbolic link called lastsnap.jpg (or lastsnap.ppm) created in the target_dir will always point to the latest snapshot, unless snapshot_filename is exactly 'lastsnap'
This option uses 
conversion specifiers which are codes that start by % and then a letter. The conversion specifiers used has the same function as for the C function strftime (3). The most commonly used are: 
-  %Y = year
  -  %m = month as two digits
  -  %d = date
  -  %H = hour
  -  %M = minute
  -  %S = second
  -  %T = HH:MM:SS
 
 
These are unique to motion  
-  %v = event
  -  %q = frame number
  -  %t = thread (camera) number
  -  %D = changed pixels
  -  %N = noise level
  -  %i = width of motion area
  -  %J = height of motion area
  -  %K = X coordinate of motion center
  -  %L = Y coordinate of motion center
  -  %C = value defined by text_event 
 
 
If you are happy with the directory structures the way they were in earlier versions of motion use %v-%Y%m%d%H%M%S-snapshot for 'oldlayout on' and %Y/%m/%d/%H/%M/%S-snapshot for 'oldlayout off'.
For the equivalent of the now obsolete option 'snap_overwrite' use the value 'lastsnap'.