An image filename does not reliably tell you its real format or dimensions. A file called small.jpg may still be too large for a form, and a renamed extension does not change the encoded content.
Image Information Inspector reads supported decoded image information. It reports dimensions, input bytes, MIME type and a sampled indication of alpha.
Separate the three size questions
A 400 by 300 image has a 4:3 ratio and 120,000 pixels. Its file bytes depend on content and encoding. Neither number tells you a physical print size without a chosen resolution.
The dimensions reflect supported orientation correction. When PHP EXIF handling rotates a sideways JPEG before inspection, the reported width and height can be swapped from its stored orientation.
MIME here comes from the image content, not just the filename. That helps identify a valid PNG or JPEG even when a browser's file label is misleading.
Sampled alpha has a careful label
The inspector checks a bounded sample for transparency. Yes means alpha was observed there. No in sample is not proof that every pixel of the full source is opaque; a tiny transparent detail can be missed.
Use an exact pixel inspection or a careful visual review when that distinction matters to an asset. Do not treat the sampled result as a forensic file analysis.
The tool does not list every EXIF tag, certify a file as safe or determine whether a photo satisfies an application policy. It also does not resize or compress the image.
Compare the reported bytes and dimensions with the destination's actual rules. If the file exceeds a pixel limit, resize it. If only bytes are too high, examine the format and compression choices instead of changing unrelated settings.