"images with at least one defect" or "images with at least a defect"?

I'm writing a technical document with some coworkers, and none of us is a native English speaker. I'm writing about images (pictures) of mechanical parts with or without defects, and I want to refer to the subset of images which contain at least a defect (possibly more than one). What's the correct form? "Images with at least one defect" or "images with at least a defect"?

"At least one defect" would suggest that you're referring to images with a minimum of one defect, but that might have multiple defects. That is, you're primarily interested in the number of defects.

"At least a defect" might be used in a context like "images with at least a defect, and possibly other quality issues" in which you're referring to many possible attributes of an image, one of which is the presence of a defect.

It sounds like you're looking for the former.