A quick and dirty (and untested) implementation would look like:
Code:
on *:SOCKREAD:sockname:{
  if ( $sockerr ) return
  sockread %temp
  if ( %temp == <request for image> ) {
    sockmark $sockname sending
    set %sendfile filename.jpg
    set %sendpos 0
    sendfilenext
  }
}
on *:SOCKWRITE:sockname:{
  if ( $sockerr ) return
  if ( $sock($sockname).mark == sending ) {
    sendfilenext
  }
}
alias sendfilenext {
  var %queuespace = $calc(16384 - $sock($sockname).sq)
  if ( %queuespace > 0 ) {
    bread %sendfile %sendpos %queuespace &temp
    sockwrite $sockname &temp
    inc %sendpos %queuespace
    if ( %sendpos >= $file(%sendfile).size ) {
      sockmark $sockname
      echo -a Sending of %sendfile complete
    }
  }
}