Please go to the Apple logo at the upper left of your computer screen to About This Mac and give me this information:
Are you using iPhoto or the new Photos?
It may not accept dragging from google but from the Desktop it should if the file is supported. Where did the photo come from? Did you see my offer to remote connect?
I can look at your screen and control your computer to see directly what is hapening...
There are a lot of things I would need to check.... what version of iPhoto, check your drive for errors, rebuild the iPhoto library etc...
Reboot into the Recovery HD by choosing the ‘Apple‘ menu > Restart, then hold down the ‘Command’ + R’ keys on the keyboard during the start up process. When you see the Apple Logo you can let go. When the machine boots you may have to choose your language then you will see the OS X Utilities screen. Select the Disk Utility and then select Continue. Then in Disk Utility select Macintosh HD in the left column (if there are two with that name or it is named something else choose the first indented item) and then on the right select the First Aid tab then select Run.
That was only one of the many things I need you to check. Open iPhoto and go to iPhoto / About iPhoto what is the version?
Apple will want to remote connect too by the way.
Quit iPhoto, hold down the Option/ALT and Command keys and start iPhoto. You will see an iPhoto Library First Aid window, select rebuild the Database.
I have El Capitan here. Any photo that is supported you can drag to "Photos" icon in the left column in iPhoto under LIBRARY. What happens when you try to do that? Where did the photos come from and what format is it? Can you send me the photo you are trying to import?
I am having trouble picturing what you are doing.. you can't drag pictures from a web browser and add them to iPhoto or Photos that has never been supported.. you can right click on a photo in a web browser and go to "Add Image to Photos" but not to iPhoto... not since Photos became the default Apple Photo editor. You would have to right click on the photo and go to Save Image to "Downloads" then drag that image to iPhoto...
What icon I really need to see your screen to help you.....???
I really don't know what you are talking about if I can't remote connect I need to opt out.