how to migrate my photos to a new iMac. do not wish to use iCloud

Hi,

That shouldn't be a problem! You will need some other way to transport the files (external hard drive, thumb drive, or even dropbox). Whatever storage medium you use to move the files it will likely need to be fairly large, depending on the size of your photos library.

First you will just need to locate your photos library, it is most likely in your Mac's Pictures folder. You can find this folder by going into the finder > Macintosh HD > Users > (your username) > Pictures. In this folder there should be a photos library file probably labeled "Photos Library.photoslibrary", or something similar.

Next just right click and copy that file and then paste it to your external hard drive/dropbox folder.

Once it has finished copying you can connect that drive to the new computer, then open the photos app. In the Photos app select File > import in the menu bar and select your photos library file that is now located on your external drive.

For more information on this step see > this support article.

I agree using an on using an External Hard Disk if all you want migrate is your photos. However if you want to do a migration of your data, apps and even settings please use Setup Assistant and Migration Assistant.

Welcome to the Apple Support Communities.

See: Set up and use iCloud Photos - Apple Support.

Jack