Recursively search for images, and move them to a date folder
Change to the folder you want to search and run

find . -type f -iname '*.jpg' | while read file; do
    ts=$(stat -f '%Sm' -t '%Y-%m-%d' "$file")
    folder="/path/to/backup/folder/$ts"
    [[ -d "$folder" ]] || echo mkdir "$folder"
    echo mv "$file" "$folder/"
done


Best to test this on a small sample first, and remove both echos if the output looks reasonable.