I'm new to kdenlive but I think it is the SW I need for my project.

My project is about creating a time-lapse animation.

I took some several hundret pictures over the last years.

I learned that kdenlive could create slideshow clips from single frames resp. my images.

But what I need is some blending between them. Ideally I need some morphing like in this clip: http://www.youtube.com/watch?v=wZurRt0TidI

Is this possible, and how?

What you're showing in this clip is based on a little bit more advanced techniques than plain image blendin ( Kdenlive could do the blending -> e.g. dissolve transition).
It involves mesh warping etc. and requires a dedicated editor to control the desired warping by
control point in source and target frame. You need to utilize tools like xmorph/gtkmorph or xmrm.

Toby