Is an EPS or AI file always a vector?

No. EPS and AI (Adobe Illustrator) are formats that can hold vector artwork. Neither one guarantees it. Either can contain a photo, a pasted-in JPG of your logo, or artwork a computer auto-traced from a picture.

What an EPS file actually is

EPS stands for Encapsulated PostScript. It dates back to the 1980s, when it was built to send artwork to printers. Inside, an EPS is a small program that tells a printer how to draw the page. That program can describe shapes (vector), or it can simply say “draw this grid of pixels here” (raster).

Because it’s a program and not a picture, most computers can’t show what’s inside an EPS without design software. Recent versions of macOS no longer open EPS files in Preview, and Windows has never opened them on its own. That’s part of why so many people end up unsure what their EPS contains.

How a raster EPS happens

• Saved from Photoshop. Photoshop can save any image as an EPS. The result is always pixels.
• A placed picture. A JPG or PNG placed in Illustrator and saved as EPS is still a JPG or PNG inside.
• Flattened effects. Some older EPS exporters turn transparency, shadows or gradient meshes into pictures, even if the rest of the artwork is vector.

The same goes for AI files

An .ai file is Illustrator’s own format, and it can hold anything Illustrator can: vector shapes, placed photos, Image Trace results, and live text that needs a font the printer may not have.

Modern AI files also include a PDF-compatible copy of the artwork, as long as “Create PDF Compatible File” was checked when it was saved (it is by default). That’s how other apps, and the checker, can read an AI file without Illustrator. If that option was turned off, most tools other than Illustrator can’t open the file at all.

How to check an EPS or AI file

• In Illustrator: open the file and choose View > Outline. Vector shapes become thin outlines. Pictures become boxes. Window > Links lists every placed image.
• In Inkscape (free): open the file, choose Edit > Select All, and look at the status bar. If it mentions an “Image,” there’s a picture in there.
• With the checker: drop the file in. AI files are checked in your browser and never uploaded. EPS files give you a choice, because the only way to see exactly what an EPS draws is to run it:
  • Private check: stays on your computer. It reads clues inside the file and gives you a likely grade, or tells you it can’t be sure.
  • Full check: your EPS is sent to our server, run with Ghostscript, measured, and deleted right after. You get a real grade and a preview with every picture outlined.

What to send a printer

If you have the choice, ask the printer what they prefer. Many shops today are just as happy with a vector PDF or an .ai file (with text converted to outlines) as with an EPS, and PDFs are easier for everyone else to open and check. Whatever you send, run it through the checker first.