wfasa on "[Plugin: Wordfence Security] infection found within a WordFence file"

Hello Julia,
Maybe it only warns when you have actually included an image, not when you have simply uploaded one? Wordfence doesn't warn you about the URL to your own site unless that URL appears in a text field (hidden or visible). In other words, it's not warning you about the images themselves, it's warning you about the URL to the image (because the URL contains a domain that has been flagged by Google Safe Browsing).