Decode base64 images into media files and replace the original file with WordPress upload folder. You need to upload the images into /wp-content/uploads/ after finishing.

convert-base64-images.sh

#!/bin/bash
file=${1}
for extension in png jpeg jpg gif bmp; do
    for image in `grep -ho "data:image/${extension};base64,[A-Za-z0-9+/=]*" ${file}`; do
        image_signature=$(echo ${image} | md5sum | awk '{print $1}')
        echo ${image} > ${image_signature}.hash
        rm -f to-replace.script
        echo "s|$(cat ${image_signature}.hash)|/wp-content/uploads/${image_signature}.${extension}|g" > to-replace.script
        sed -i -f to-replace.script ${file}
        sed -i "s|data:image/${extension};base64,||g" ${image_signature}.hash
        cat ${image_signature}.hash | base64 -d > ${image_signature}.${extension}
    done
done