First & foremost Marc WOW! Fantastic illustrations.

I can only confirm that on my iPhone there are just black boxes where the images (thumbnails) should be. Clicking on one does correctly open the HighSlide image correctly however, which isn't much use without the thumbnail image though It's also the same on the Android tablet I have.

Perhaps you could attach a cut down version of the site as a xar file so we can have a look-see?

As an aside on your Info page you have:

His partipation at artistic events has also been recognized with international awards
I think you mean participation?