Unless something has changed in Tiki 1.74, the Image Galleries depend on the GD or ImageMagick libraries. My unfortunate experience is a hosting where the first works badly (some versions - unlucky!), and the second is waiting (3 months!) for someone to install it correctly. Everything apparently works but there's no thumbnail or picture. Windows doesn't have the libraries though I think I've got a version of ImageMagick for Windows somewhere.

No, I hadn't read the whole document. Shame on me! You did mention GD and ImageMagick!

But there can be another problem arising (for me, for example) from folder permissions so the images can't be imported through the default temporary folders. Code has to be modified. Thanks again Markku for your help with this.

This page fails to mention that when you are logged in as a non-admin user, the create gallery page does not give you the option to show to non-admin users. So when a user creates a gallery, it does not show up in the list of galleries, letting the user think that there is an error somewhere.