I want to make a template with placeholders for some text and pictures, but I want all the pictures to be the same size. Is there any way to make a placeholder with a locked size, so when I use it to insert a picture, it’ll have that size (width or height)? Could I use frames in any way?
I made a quick test with frames and it works. In a frame you can add
- only a picture
- only a text
- a picture and text
and you also can add a caption to picture inside the frame.
note: you can set each frame at a different size should you want to do so.
Thanks. Could it be combined with placeholders? When I tried, the images didn’t fit in the frame. Could the frame size be locked so all images automatically is resized so they fits (either height or width so it keep propotions)?
You can use an “Image Control”. That will automatically generate a form, but don’t worry, you do not need to use a data base. A form has a “Design mode” where you can edit its controls. Use the icon “Design Mode On/Off” to toggle the state.
View > Toolbars > Form Controls, and there the icon “More Controls”. 
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While in “Design mode” click on icon “Image Control” and drag create it same as it would a rectangle. 
Such control has an edit mode with green handles, where you can set position and size. If you need further settings like border style and color or help texts, open the item “Control” from the context menu. In that dialog you can set the scaling properties in tab “General”, item “Scale”. You can chose between “none” (original picture size), “keep ratio” (picture is scaled to control size while keeping its ratio), and “Fit to Size” (picture is stretched to the control size). Default is “keep ratio”, which meets your purpose.
When you have saved the file and reopen it or when you generate a document based on the template, then the form is no longer in Design mode. If you now right click the Image Control, you get the option “Insert Graphics from…” to fill the control. As usual, you can chose between embedding or linking the picture. The attached file is an example of such template.Example Image Control.ott