There is another date time stamp with the exif data, if present, showing the date created on the machine as you say or the date modified. But the original creation date remains the same. (No, not quite, as explained below when I saved the photo to my desktop to see what would change in the exif, if anything).
Here goes formatting headache), a cute cupcake photo from my Canon EOS-20D which does not record GPS (some phones and newer cameras do).
Here is what exif data looks like. The Image Created was what the camera recorded when the photo was taken. The Image Generated and Image Digitized below info are the same, a little later from the time taken and were recorded by Photoshop when I processed the photo.
So I open the photo in Photoshop again and save it again to my desktop. The Image Created date and time are changed to today, but the Image Generated and Image Digitized info remain the same as when I processed the photo originally. The original camera date taken and time data are lost, but I keep all my original photos as shot in .CR2 (RAW) format in different folders and can recover that easily.
But I didn't know which date changed! I knew it also changed something if I move to another computer. Different cameras may have slightly different info.
File name: Cupcake_2_Go.jpg
File size: 140551 bytes (800x600, 2.3bpp, 10x)
EXIF Summary: 1/400s f/6.3 ISO400 100mm (35mm eq:160mm)
Camera-Specific Properties:
Equipment Make: Canon
Camera Model: Canon EOS 20D
Camera Software: Adobe Photoshop CS5 Macintosh
Photographer: unknown
Maximum Lens Aperture: f/4.0
Image-Specific Properties:
Image Orientation: Top, Left-Hand
Horizontal Resolution: 72 dpi
Vertical Resolution: 72 dpi
Image Created: 2012:08:23 17:38:42
Exposure Time: 1/400 sec
F-Number: f/6.3
Exposure Program: Aperture Priority
ISO Speed Rating: 400
Lens Aperture: f/6.3
Exposure Bias: 0 EV
Metering Mode: Pattern
Flash: No Flash, Compulsory
Focal Length: 100.00 mm
Color Space Information: Uncalibrated
Image Width: 800
Image Height: 600
Rendering: Normal
Exposure Mode: Auto
White Balance: Auto
Scene Capture Type: Standard
Other Properties:
Resolution Unit: i
Exif IFD Pointer: 228
Compression Scheme: JPEG Compression (Thumbnail)
Horizontal Resolution: 72 dpi
Vertical Resolution: 72 dpi
Resolution Unit: i
Offset to JPEG SOI: 730
Bytes of JPEG Data: 8684
Exif Version: 2.21
Image Generated: 2012:08:23 17:28:13
Image Digitized: 2012:08:23 17:28:13
Shutter Speed: 1/400 sec
Focal Plane Horiz Resolution: 3959 dpi
Focal Plane Vert Resolution: 3959 dpi
Focal Plane Res Unit: i
I know. The exif info posted however lacked nearly everything, IIRC the only info was create date, which was today.
I downloaded many copies of the hotel photo and all had the xif info stripped.