slider or static image on all pages

For that you can use conditional tags. You can read more about theme here.

Here is a basic example how you can use conditional formating to target specific page title, id or even page slug. So you can place whatever image you want on any page you want via header.php file.

<?php
if (is_page( 'Front Page' ) ) { // page title
	echo '<img src="https://image1.jpg" alt="alt text">';
}
elseif (is_page('44')) { // page id
	echo '<img src="https://image2.jpg" alt="alt text">';
}
elseif (is_page('about-me')) { // page slug
	echo '<img src="https://image3.jpg" alt="alt text">';
}
else {
	echo '<img src="https://colorlib.com/wp/wp-content/uploads/sites/2/colorlib-logo-top.png" alt="">';
}
?>

thank you. it works now. ??

But there is another question related to this…

there is my site, it will be easier to follow my question https://gaprodesign.si/vaja/
For my main menu I choose pages and categories. For example: ‘O meni’ and ‘Kontakt’ are created as pages, because there are static information, ‘Aktualno’, ‘Moje delo’ and ‘Sporo?ila za javnost’ are created as categories, because here you will add post and assign it category and it will show in each category… so to get header image work I change is_page to is_category and it works. so far is everything ok.:)
but when I click on post, to read the whole post I loose header image.
how can I add header image for every post in every category…?

In this case you can use in_category

Let me know if this helps.

Hi.
That is working now! Thank you.

But I have another question. On my Category page there are posts, like list of posts with short content, and than you click on post and you can read the whole content.

Is it possible to show images that are included in posts on category page, next to short content?

I included post-thumbnails (feature image) and set display:none for single post, so I cant see feature image in my post.

But when I did this the width of text next to the thumbnail got smaller and the button ‘continue reading’ is in same line…
I want to have thumbnail (150px x 150px) and than text full width and button under it like in case there is no image…

Thank you