iMac won't recognize my iPhone to upload pictures When I plug my iPhone into my iMac via USB, Dropbox tries to access the pictures, but won't download them. iTunes recognizes the iPhone, but doesn't have a selection to import pictures, only videos. iPhoto doesn't even recognize the iPhone.

My iMac is running Mac OS 10.13.5 and my iPhone has the most recent iOS update.
The Image Capture app is designed to allow you export images from your iPhone to your iMac. The Photos app can also do this, but then you will need to learn how the Photos app works. 

Both apps are found in the Applications folder.