The card is one that is almost 1" wide by 1 1/4" long. I am thinking it must be in the CD drive.
There's a very very BIG difference between the size of the CD drive slot and the SD card slot (mentioned in post #1). Can you please confirm which one it is??
I'm pretty sure as well that it's the CD drive slot...since a full sized SD card can't get "lost" in the SD card slot that it was designed for.
Only thing I can suggest is DON'T DON'T DON'T insert any DVD's or CD's into the slot with an SD card "lost" in there. This may only make things worse!!!
Turn the computer on it's side (so the slot is facing downwards)...and try to hear if the SD card is moving/jiggling around inside. If it is...try to get it to fall towards the slot. If you can get the SD card just on the other side of the slot...you may be able to CAREFULLY "fish" it out with a thin piece of plastic (like a plastic knife or credit card)...or maybe & carefully try a paperclip (don't insert the paperclip too far).
If the SD card is stuck somewhere in there (can't hear it moving or jiggling)...then this issue is going to require more serious surgery.
Of course the iMac is a bit big & awkward to have on it's side while trying this...so you will probably need a 2nd person to help.
- Nick