How can I transfer photos from a 2009 iMac to a flash drive?

hello, so i made a post with this same title about a month ago (How can I transfer photos from a 2009 iMa… - Apple Community). i’ve since tried everything recommended in that thread that i’m actually smart enough to do.

i found the originals folder under my iphoto library. some of the pictures in my iphoto gallery are there and some aren’t. i was able to copy and paste the ones in that folder over to a flash drive. the ones that aren’t in the folder and seemingly just exist in iphoto cannot be copied and pasted over because “one or more of the items may have been deleted or are no longer available” am i just out of luck with these particular photos? is there genuinely no way to save them?