A contact sheet is for reviewing a set of pictures, not forcing every one into the same cropped composition. Keeping the whole source makes it easier to compare framing and decide which file to use next.
Photo Contact Sheet fits images into preview cells and labels them by input number. It accepts up to six sources in their upload order.
Preview space and label space are separate
With three columns, 240 pixel cells and 16 pixel gaps, the canvas width is 784 pixels. A row also includes a 24 pixel label area below each preview cell.
For two uploaded images in that one row, the height is 296 pixels. The unused third cell area remains part of the layout's background.
A portrait and a landscape image both fit inside their square preview cells. Empty space is expected because the complete image is retained rather than cropped to fill the cell.
Numbered labels are not original filenames
The labels identify Image 1, Image 2 and so on. Keep the upload order clear if you need to refer back to the source files after sharing the sheet.
A contact sheet is a resized visual summary. It does not preserve enough resolution to inspect every detail of a larger source or replace the originals in an archive.
Choose a cell size that makes the intended differences visible. Very small cells can hide a blurred face or make nearly identical product photos difficult to distinguish.
The output is one image with the selected background. If you need a tightly filled promotional grid instead, use Collage and inspect its crop tradeoff. For a review sheet, the visible padding is useful because it shows that the full source is still represented.