Upload an image to see its pixel dimensions and any stored resolution metadata, then work out its effective PPI at an intended print width.
Pixel dimensions come from the decoded image itself. Stored resolution is read directly from the file bytes: the density segment of a JPEG JFIF header, or the pHYs chunk of a PNG, both parsed manually. Many images, especially screenshots and web exports, store no resolution at all — in that case the file simply has no DPI to report, and print sharpness depends on pixel count and print size instead. The effective-PPI figure divides the image width in pixels by the intended print width in inches.
Why does an image show no stored DPI? Because the file does not store any. Screenshots, phone exports and many web images carry pixel dimensions only, and print software then assumes a default such as 72 or 96 PPI.
Is 300 DPI required for print? 300 PPI at the final print size is the usual target for sharp close-up print. Posters viewed from a distance look fine at far lower effective PPI.
Does changing stored DPI change image quality? No. Editing the stored resolution only changes the default print size the pixels map to. The pixel data, and therefore the detail, stays the same.