jpg vs JPG

Upper case doesn't make a difference to Windows. A search will confirm this. I did a quick look at some of my photos. I have thousands and they're a mixture of .jpg and .JPG and I don't have a problem opening either in IrfanView or FinePix Viewer. What are you using to open the files? How are you receiving the photos? The JPG files might be a proprietary or non-standard format. (Or maybe not really JPG) If you have a file hex viewer, you can look at the file header. Hex bytes 7-10 should look like this: 4A 46 49 46 or J F I F in character mode.

I encountered something similar while using XnView. While using the XnView browser filtered only for images, the jpg extension files were not acknowledged. What finally clued me in the right direction was the properties of each file. I had to rename the extension for the proper picture format that XnView identified. Your wife's machine's ability to open these files complicates matters. However, from windows explorer, right-click the file and select properties from the context menu. From near the top of the properties window, there is "open with" and "change".

armyslowrdr said:

maybe not to the OS, but I know without doubt that to a web-host, specifically tripod, it matters.

t-4-2 said:

....

File extensions are NOT case sensitive.
......

Care to explain .....
What " tripod " or " web-host " for that matter, has got to do with the OP's inability to open JPG files from the Windows Explorer ?