A photo has a fixed pixel count. Printing those pixels larger reduces effective resolution. Use the original file rather than an image saved from messaging or social media, place it at final size, and inspect both warnings and fine details.
Print viewed up close needs more detail than a large banner seen from a distance. Merely changing the DPI field or saving a small JPG as PDF does not add detail. A vector PDF is usually best for logos and line art.
Inspect faces, small type, fine lines and diagonal edges. If uncertain, tell support the pixel dimensions and intended print size so the effective resolution can be assessed.