1Drop the whole set in
Up to 20 pictures. They keep the order you dropped them in.
2Let them finish
Each one is compressed first, so the sheet is built from small files rather than from the originals.
3Pick a layout and save one picture
Collage, or squares in a grid. Download one JPEG, or a single-page PDF of the same thing.
Questions
How do I combine several photos into one picture?
Drop the whole set in together, let them compress, and the combined picture appears on the page as you change it. Choose a collage and the rows are fitted to the width so nothing is cropped and there are no gaps between the pictures; choose squares and every photo becomes one, either cropped to fit or shown whole. Then download it as a single JPEG, or as a one-page PDF.
Can I make a photo grid or an image grid?
Yes — that is the squares layout. Every picture is given a cell of the same size, laid out in as many columns as you choose or as many as suits the count, and you decide whether each photo is cropped to fill its square or shown whole with space around it. A collage is the other option, where pictures keep their own proportions and the rows are what get adjusted instead.
How do I put screenshots side by side in one image?
Drop them in together and pick the collage layout with spacing set to none, which butts them against each other with no border. Two screenshots come out side by side; more of them wrap into rows that each fill the width. Switching the filenames on is worth it for a bug report, since it gives whoever reads it a name to quote back at you.
What is a contact sheet?
One picture with a whole set of pictures laid out on it. It comes from film: a photographer would print a strip of negatives at actual size onto one sheet so the roll could be reviewed and individual frames chosen without printing them all. Proof sheet and index print are the same thing under other names. The digital version is used the same way — to look at a set, and, with the filenames switched on, to have a name to point at when you want to talk about one of them.
How many pictures fit on one sheet?
Up to 20 here. The grid is worked out from the count unless you choose one: nine pictures come out three across, sixteen come out four across, and past that the columns stop at six because thumbnails narrower than that stop being recognisable, which is the only job a sheet has.
Can I put the filenames on the sheet?
Yes, with one switch, and they are off to begin with. Most sheets are made to be looked at or posted, where a filename written under every picture is clutter. Turn them on when the sheet is going to somebody who has to reply about one particular shot — that is what makes it a proof sheet rather than a collage. A long name is shortened from the middle rather than the end, because the identifying part of a camera filename is usually at the end.
Are my pictures cropped to fit the grid?
No. Each one is fitted whole inside its cell, so a landscape shot and a portrait shot both keep their shape and you see the entire frame. Filling the cell instead would look tidier and would cut the edges off most of the set, which usually removes the part that says what the picture is of.
Can I print it?
Yes. Download it as a JPEG, or use the PDF button, which puts the whole thing on a single page sized to the picture rather than one page per photo. It is built at a size meant for looking at rather than for a large print, so a sheet of twenty fills a page comfortably and will not hold up to being enlarged much past that. For print resolution, use fewer pictures per sheet.