s/cid:image002.gif@01CC3D46.926E77E0/https://mysite.com/files/1922/g
s/cid:image003.gif@01CC3D46.926E77E0/https://mysite.com/files/1923/g
s/cid:image004.jpg@01CC3D46.926E77E0/https://mysite.com/files/1924/g

while read cid fileid
do
    cidpat="$(echo $cid | sed -e s/\./\\./g)"
    echo 's/'"$cidpat"'/https://mysite.com/files/'"$fileid"'/g' >> sedscr
done

escaped_lhs=$(printf '%sn' "$lhs" | sed 's:[][/.^$*]:\&:g')
escaped_rhs=$(printf '%sn' "$rhs" | sed 's:[/&]:\&:g;$!s/$/\/')

sed "s/$escaped_lhs/$escaped_rhs/"

A=lhs B=rhs perl -pe 's/Q$ENV{A}E/$ENV{B}/g'