For directory (folder), only read is not enough. You need to set execute also. Because for directory, execute means you can enter the directory.

Files need read permission & directory needs read & execute permission.

So the directory permission should be: 0555. However, image files inside that directory should be just read, in numeric form: 0444.

For example, in your case, /legacy-images/ directory will have 0555 permission & /legacy-images/image1.png image file will have 0444 permission.

Shell Command

If you can access shell and know how to, you may use the following shell commands (replace <WP_DIRECTORY> with appropriate WordPress installation directory):

cd <WP_DIRECTORY>
chmod 555 legacy-images/
cd legacy-images/
find ./ -type f -exec chmod 444 {} \;