[ImageSize]

Thank you very much. I've made it.

<div><img alt="" src="../Images/NameofImage.png" width="100%" /></div>

This version always stretches the image to 100 %. Thats not what I want.
Also that:

img {
width: 100%;
}

But

img {
max-width: 100%;
}

should do it. I write should, because Aldiko has a bug, where this doesn't work.

So the workaroud for Aldiko that it shows the images in the right size is to add to each <img> tag

style="max-width:100%"
Example: <img src="main-7.png" alt="" style="max-width:100%"/>

Now it works even with Aldiko. You can use Notepad++ and the function replace in files.

<img src=(.*?) style=(.*?)/>
<img src=\1/>

This is the first Regex. With that you remove the
style="width:###pt;height:###pt;" which makes Abby.

After that you use

<img src=(.*?)/>
<img src=\1 style="max-width:100%"/>

And now all your images are correctly displayed.