Where did these THM files come from?

I've just noticed loads of THM files in one of my folders. As I understand it these are thumbnail 'sidecar' files to the main CR2 files from my 400D. Are they important? Can I delete them or will it cause problems?

The odd thing is they only appear from a 2 week period this month. The images I got today don't have them nor do ones from last month and before. I don't recall changing any settings or anything (although I downloaded the Apple RAW update this morning, maybe it's something to do with that).

I've been using Image Capture on Mac OSX (10.5) to download images onto my computer.

Weird that they suddenly appeared. They can only be opened with the Canon Viewer (from Photostitch).

Edited to add:

They now appear whenever I open RAW files in DPP..............

My understanding is that the THM files are a record of changes made in ACR to a RAW file, so that when you open the RAW file a second and subsequent times, you effectively have a log of the changes you made in ACR, which is opened at the same time.

You can delete the THM files, but if you open any RAW files you have previously worked on, they won't open in ACR with the settings you last used.

I think that's what they are anyway, if I'm wrong I'm sure someone will be along to correct me.

Thanks for the quick reply.............but actually I never use ACR (DPP mainly as a RAW converter, sometimes Aperture).

I'm pretty sure you can remove the THM files. They're just thumbnail preview files from what I know. You normally see them on P&S cameras (normally they're video thumbnail files).

Sizecar files to CR2 files are usually .XMP files.

Have your storage cards been used for any other purpose than in your 400D?

Pete wrote in post #6325206
I'm pretty sure you can remove the THM files. They're just thumbnail preview files from what I know. You normally see them on P&S cameras (normally they're video thumbnail files).

Sizecar files to CR2 files are usually .XMP files.

Have your storage cards been used for any other purpose than in your 400D?

I just deleted them............and nothing seems to be affected.

My cards haven't been used for anything except in my 400D. The THM file numbers matched the CR2 files over a 2 week period. Maybe I accidentally changed some preference somewhere.

I've noticed XMP files when i use ACR. Just never seen THM before.