Start with the pictures in your composition
A set of photographs and a sequence of text-heavy screenshots can need different export choices. There is no format that is always the best for every composition. Decide where the image will be used and what must stay readable before saving.
Consider JPEG for photographs
JPEG can be a practical sharing format for photographic images. Check faces, fine detail and the size of the saved file. Compression may change detail or introduce visible artifacts, so keep the original photos for future edits instead of treating the collage as a replacement for them.
Consider PNG for text and graphics
PNG avoids the lossy JPEG compression that can affect crisp text and graphic edges. That does not guarantee a small file, nor does it add detail to an already low-resolution screenshot. Inspect text at the final output size and check the file size if you plan to send it as an attachment.
Choose the output in Combine Photos
Arrange two to thirty images using one of eleven layouts, then choose JPEG or PNG for the export. The app supports output up to 3000 pixels wide. Before saving, check framing, image order and spacing. One free export is included; further exports require eligible Pro access.
Verify the destination too
Open the saved image before sending it. Then check the copy received by the destination, because a messaging or publishing service can resize or recompress an uploaded image. If text has become too small, simplify the composition or choose a file delivery method suited to the detail you need.