BASALT · JOURNAL
Turning photos and scans into a single PDF on a Mac
You photographed eight pages of a contract with your phone and someone needs one PDF. The Mac has several ways to do this, and most get page order wrong, orientation wrong, or quietly re-encode images that were already compressed.
What the conversion is doing
A PDF page containing a photo is a small object: a /Page with a MediaBox, a content stream of a few dozen bytes that sets a transformation matrix and paints one image XObject, and a reference to it in the page's resources. The image itself is a stream with a filter naming its encoding.
That last detail matters. If the source is a JPEG, its compressed bytes can be embedded directly as a DCTDecode stream with no decoding step, so the page holds your original JPEG unchanged and the conversion is lossless.
If the tool instead decodes to a bitmap and re-encodes, you have taken a generational loss for nothing: the picture is worse and the file usually larger. HEIC photos always require a decode, since PDF has no HEIC filter, but that transcode should happen once at a quality you chose.
Page size, and why phone photos come out wrong
An image has pixel dimensions and sometimes a DPI value in its metadata. A PDF page is measured in points, where 72 points is one inch. Converting requires deciding how those relate.
Three policies exist. Fit each image to a fixed page size such as US Letter or A4, which is what you want if the output will be printed or filed. Size each page to the image, using its DPI if present, which preserves the image but produces varying page sizes. Or fit to a fixed size preserving aspect ratio, the usual compromise.
Phone photos are where this shows. A 4032 by 3024 photo with no meaningful DPI tag, sized at 72 dpi, becomes a page 56 inches wide; fitted to Letter it is readable. If your document opens at an absurd zoom or prints across sheets, this is why. Mixed sources make it worse, since phone photos, a 300 dpi flatbed scan, and a screenshot have three different natural page sizes.
Orientation and the EXIF trap
A photo taken in portrait is often stored as a landscape bitmap plus an EXIF Orientation tag telling the viewer to rotate it. Preview and Photos honor that tag, so the picture looks right on your Mac.
PDF has no equivalent. The image goes into the page as pixels, and if the converter ignores EXIF Orientation the photo lands sideways in a document that looked fine in Finder. A correct converter reads the tag and either rotates the pixels or applies the equivalent transformation matrix in the content stream.
Check every page of the output, not just the first, since a batch can mix orientations. If pages come out wrong, rotating pages on a Mac covers what /Rotate does.
Page order
Batch conversion takes files in some order, rarely the one you expect. A directory listing sorts lexically, so IMG_10.jpg comes before IMG_2.jpg, and files copied off a camera may carry creation timestamps that differ from capture order. Decide which ordering you want before converting, then verify rather than trust: a twelve-page contract with pages 10, 11, and 12 between pages 1 and 2 is the classic outcome.
The built-in Mac options
Preview converts images. Open the files together, select all thumbnails, choose File then Print, then Save as PDF from the dialog's PDF menu. It works, but the print pipeline rasterizes at print resolution and applies the dialog's page setup, so you are not embedding your original JPEG data.
Finder's Quick Actions offer Create PDF for selected images, faster but with ordering following your selection and page sizes following the images. Automator's New PDF from Images does the same in a workflow. None of the three give control over encoding, page size, or margins, or report what they did. sips is worth knowing for preparing images first, since it normalizes a folder of HEIC files into JPEGs with orientation baked in.
After the conversion
An image-only PDF has no text layer, so it cannot be searched, quoted, or cited. If the document will be used rather than filed, run OCR, which adds an invisible text layer over the image while leaving the picture visible. It is also a prerequisite for redacting a scanned document.
Photos also carry metadata that survives into the PDF if the converter copies it, including GPS. If the document is going outside your organization, strip it, as covered in removing PDF metadata on a Mac.
Frequently asked questions
How do I convert images to a PDF on a Mac?
Select the image files in Finder, right-click, and choose Quick Actions then Create PDF, which produces a single PDF in the same folder with one page per image. Alternatively, open them in Preview, select all thumbnails, choose File then Print, and pick Save as PDF. Neither gives control over page size or encoding, so check the output first.
How do I combine multiple photos into one PDF on a Mac?
Select all the photos in Finder in the order you want, then use Quick Actions then Create PDF, which creates one document with each image on its own page. Check the page order afterward, because file listings sort lexically and IMG_10 sorts before IMG_2. If the order is wrong, reorder the PDF's pages rather than converting again.
Why are my photos sideways in the PDF?
Because the photo was stored as a landscape bitmap with an EXIF Orientation tag and the converter ignored it. Preview and Photos honor that tag so the image looks correct on your Mac, but PDF has no equivalent, so the pixels go in as stored. Use a converter that reads EXIF Orientation, or rotate the pages afterward.
Can I convert HEIC photos from my iPhone to PDF?
Yes, and macOS handles HEIC natively, so Preview, Quick Actions, and Automator all accept them. The images must be decoded and re-encoded, since PDF has no HEIC filter, meaning one transcode whose quality you should control. Converting to JPEG first with sips gives that control and bakes in orientation.
Does converting images to PDF reduce the image quality?
It depends on the tool. A converter that embeds JPEG data directly as a DCTDecode stream keeps your original bytes and loses nothing, while one that decodes and re-encodes takes a generational loss and often produces a bigger file. Preview's print route rasterizes at print resolution rather than embedding the original.
What page size should I use for scanned images?
Fit to a standard page size such as US Letter or A4 if the document will be printed, filed, or read alongside others. Sizing each page to its image preserves the original but produces inconsistent pages, jarring across a batch of phone photos, flatbed scans, and screenshots. Fit-to-page with preserved aspect ratio is the usual compromise.
Can I make the resulting PDF searchable?
Not from the conversion itself, since an image-only PDF contains pixels and no text objects. You need OCR afterward, which adds an invisible text layer over the image so the page looks unchanged but can be searched, copied, and cited. Run OCR before compressing, because recognition on downsampled pixels is less accurate.
Do photos keep their location data when converted to PDF?
They can. Photo files carry EXIF metadata including GPS coordinates, camera serial numbers, and timestamps, and some converters copy that into the PDF's metadata or leave it in the image stream. If the document is leaving your organization, check and strip it, since a site photo can disclose where and when it was taken.
Doing it in Basalt
Basalt turns photos into a PDF and writes it as a new file, leaving your source images untouched. Because it sits alongside OCR, compression, and metadata cleanup among 18 tools in one window, you can convert, make the result searchable, and strip the photo metadata before it goes anywhere. Everything runs in a sealed engine process with no network entitlement, enforced by macOS at the code-signature level, so your photos never leave the Mac. It is a 17 MB download for macOS 13 and later, Apple silicon and Intel, $29 once for up to three Macs with a 24 hour free trial, at basaltformac.com.
Redaction that proves itself
Basalt destroys the content you mark, then re-opens the file it wrote and proves the content is gone before it saves anything. Your documents never leave your Mac.