if we have pictures with a resolution of 300 ppi and insert these to InDesign and we adjust the size to the layout, the resolution is sometines inefficient and the pictures have to be changed in PS. Is there another possibility, because the final size can only be adjusted in InDesign?
It's not really clear what you're asking , but be assured there's nothing mysterious in play. When you Place (using File > Place) an image into your InDesign layout, its resolution is honored, and subsequently factored inversely by any scaling you apply on the InDesign page. In other words, Place a 300ppi image and then double its size. This will result in an "effective resolution" of 150ppi, as can be confirmed by checking the Info panel with the image selected. Conversely but likewise, scale it down to half its original dimensions, and see an effective resolution of 600ppi.
If this still leaves your question open, please rephrase it.
As long as the image is the same size as the Photoshop .psd or smaller, you'll be fine. It's scaling up that causes the problem. As per John's response above, select the image, and choose Window > Links. Look at the bottom half of the panel for the effective PPI. That's going to alert you to a potential problem. In the 3 figures below, the one on the left shows the image is the original size, in the middle, scaled to twice the original size, and on the right, scaled to half the original size. You can see how scaling impacts the effective PPI, and therefore the output.
the resolution is sometines inefficient and the pictures have to be changed in PS.
As Barb and John note—in the layout pixels are scaled along with the image. You can however down sample to a target resolution on export. So if you want the final output resolution to be a uniform 300ppi, make sure the starting (Actual) resolution is high enough that scaling up keeps the effective res over 300ppi.