Can I reuse my published images I have written respectively co-written papers where we have added images to illustrate our contribution. The images are far from technical and show prototypes in the field of HCI. It is not uncommon to write follow-up papers, especially of latest braking publications.

A publisher has asked us if we had previously published any illustrations and if we had secured all copyrights for them. As we own the illustrations but have published them before in a copyrighted paper respectively article, would we be able to reuse them?

I have looked at some publisher's copyright statements but they mostly refer to the paper, not the images. Would the latter be considered part of the publication and, therefore, be implicitly also copyrighted by the publisher?
In the context of an academic publishing agreement, the "paper" almost certainly includes everything on the page including the images, but read the agreement carefully. If you handed over the copyright of your images, then you'll need to secure the right to reusing them from your original publisher. This is usually easy.