what does that black arrow in my desktop mean?

Hi.

It sounds like the icons are not the image files themselves, but are aliases that point to the location of the original files. If you select one then press ⌘I (command-i), what Kind does the Get Info window say the file is? An Alias?

Where were the original files that you wanted to download? Were they on an SD card or in a camera?

It looks like the files themselves were not copied, but aliases were created that point to the original files that still live on the source media. You might try copying the original files from the image capture again.

I hope this is helpful.

Where do the pics come from, how are you downloading them to your computer, and where on your computer are you putting them? Pics should go into the /Home/Pictures/ folder. The "alias" tag usually occurs when you are trying to move the files out of a folder you don't have permission to use even though you may be an admin user.

Does your computer have an SD slot? If not then how are you getting the pictures from the SD card to your computer? I don't think you can transfer pictures from an SD card to your computer using a printer.

It appears that you need to understand how your printer handles the SD card, and whether it actually makes the data on it available for manipulation on your iMac.

Check the user manual or guide for the printer and see what is required to offload the data from the card to your iMac.

If nothing else, you can purchase a USB SD card reader which will allow you to plug the card directly into the iMac USB port, mount the SD card on the desktop as would a flash drive, and copy the files direrctly that way, without having to go through the printer interface.

For example... Pixelflash USB SD card readers

It means those are "aliases" rather than the real files.

🙂