Use alternate scaling of the image if there is empty space available

I write a book with several chapters. Every chapter contains several (floating) images, usually photos in standard landscape-style, therefore they are scaled to the size of 0.4textheight so that at least two images fit to the page with the captions (to save space).

I use the following function “photo” for adding photos:

newcommand{photo}[3] {
begin{figure}[htbp]
begin{center}
leavevmode
includegraphics[height=0.4textheight]{#2}
end{center}
caption{#3}
label{foto:#1}
end{figure}
}

However, it often happens that on the very last page of the chapter only one (last) image is shown. As I’m using the scaling, it scales the image to the same 0.4-size, which in this case is not needed, as the remaining part of the page is left empty anyway (end of the chapter), and even scaling up to 0.9textheight would be possible.

The problem is that I don’t know whether the photo is floated to the end of the paragraph or not. Or, is the photo positioned to the last page filled with some text also or with lots of free space available.

The book is actually generated by the program (it is a family tree book, automatically split into chapters), I don’t want to edit this manually.

So, is there an option in Latex (LuaLaTex) to

• scale the images to the requested size normally, but
• scale the image up to fill the page in case there is empty space available anyway.

(In short, the scaling should depend on the position where the photo is placed after floating.)

newcommand{photo}[4][0.4]{
begin{figure}[htbp]
begin{center}
leavevmode
includegraphics[height=#1textheight]{#3}
end{center}
caption{#4}
label{foto:#2}
end{figure}
}