I am creating a practical guide book with images. I am using Scrivener. I need to include images into the text, but I will then pass over my draft to a layout designer to layout out the project in Indesign. Should I bother putting full size images into Scrivener, or should I just put placeholders in and then hand over the full size images to the designer?
As a user of both programs, I would definitely say just put in a placeholder and let your designer import the images. Having them in the Scrivener text isn't going to help. You export them as Word or whatever, and then as a designer I'm going to strip out everything but the raw text so I can style and format it properly in InDesign. I'd much rather you put [PLACEHOLDER] so I can find it easily.
If you want to include instructions about size, text wrap, alignment, etc. by all means do so, but don't bother sticking the image into your Scrivener document.
The only advantage I can think of to including the images in the file you submit to the designer is so that the designer can then see exactly which picture you want placed where. It seems a lot easier to include the image than to say, "put the image with the blue cat right here" or "use image MVC3675 right here." Either way the designer will have to either remove the note from the text or fix any bugs that arise from including the image.
What I wouldn't worry about is formatting the image at all (including borders, shadows or other visual decorations). Don't try to make it look exciting. Just make sure your formatting is simple and consistent (think high school English paper). Also submit the high resolution files separately! The designer won't be using images directly from your word processing file (it seems like you know these things, but I've seen people do them before).
Another idea is to consult a style guide like the Chicago Manual of Style. They have a whole section on how to submit a transcript for publication. You could also ask the designer his or her preference.