Drop an image into a metadata viewer and a lot of people expect to see the camera model, the exposure settings, maybe even the GPS coordinates of where it was shot. That's a specific, deeper layer of data called EXIF, and it's not the same thing as the basic file metadata your browser can read. Knowing the difference saves you from misreading what a tool is actually telling you.
What 'metadata' means for an image file
At the most basic level, every image file carries a small amount of information alongside the actual pixel data: its file size in bytes, its MIME type (the format identifier like image/png or image/jpeg), and once it's decoded, its width and height in pixels. That's the layer a browser can read from any file you select, without needing to parse the file's internal structure. It's useful for quick checks -- confirming an image is actually the resolution you think it is, or catching a mislabeled file -- but it stops there.
File size isn't the same as pixel dimensions
These two numbers get confused constantly. A 4000x3000 pixel image can be a 500KB heavily compressed JPEG or an 18MB uncompressed one -- the pixel count tells you the canvas size, the file size tells you how much data was used to store it. If you're trying to figure out why an upload is rejected for being 'too large,' check the file size in bytes, not the dimensions. If you're trying to figure out why an image looks blurry when enlarged, check the dimensions, not the file size.
MIME type: why the extension can lie
A file named photo.jpg isn't necessarily a JPEG. The MIME type is determined by the file's actual content signature, not its name -- so renaming a PNG to end in .jpg doesn't convert it, and a metadata check will still report the true underlying format. This matters when you're debugging why an image won't load somewhere that's strict about format: the extension might say one thing while the browser reads another.
The 'Last Modified' trap
Most basic metadata views include a last-modified timestamp, and it's tempting to read that as 'when the photo was taken.' It isn't. It's your device's filesystem timestamp for that file -- it changes if the file gets copied, re-saved, or synced through a cloud service, none of which has anything to do with when the shutter was pressed. The actual capture date, if it exists, lives in EXIF data embedded inside the file itself, not in filesystem metadata.
Where EXIF actually lives, and why it's separate
EXIF tags -- camera make and model, exposure settings, and sometimes GPS coordinates -- are embedded inside the image file's own binary structure, written there by the camera or phone at the moment of capture. Reading them requires parsing that structure specifically, which is a different job from reading the basic file properties a browser exposes automatically. That distinction matters for privacy too: a photo can carry embedded location data that a simple viewer won't show you, and won't strip either. If you only need to confirm a file's size, format, and dimensions before you use it somewhere, the Image Metadata Viewer reads that instantly and locally in your browser.