Quality warning when making an image bigger

Just to add to what Derek and Barb suggested the Links Panel does not default to showing the Actual and Effective resolutions for images. To add that capability to the links panel you must go to the Panel Options in the Links Panel pull-down menu.

In the dialog window that opens you can check the options for actual and effective resolution to be shown both as a column next to the names of your links and in the links info that can be shown below the list of links. After you check these options they will appear as shown in the right picture above. Just to be clear Actual resolution is what you would see if you checked the resolution in Photoshop at its original size. Effective resolution is the resolution that a change in size will result in. In my experience most printers prefer that the actual and effective resolution match. Which means that the art is sized to appear in InDesign at 100% size with an actual and effective resolution of between 250 and 300 ppi. (This does vary for some specialty kinds of printing. For instance, large panels or posters that will not be viewed up close can use a lower resolution). By doing the sizing before sending the job out it decreases the amount of rip time as well as assuring that the size change has already been made to the image. As always, consult with your printer as to their specific needs.

So, how could I know this in Indesign?

The way you know this in InDesign is:

a.) by understanding in advance that when you enlarge a bitmap image you will decrease resolution

b.) by learning in advance what the minimum resolution needed is by your printer

c.) keeping the Links panel open and one eye on the effective ppi.

d.) if you can't remember to keep an eye on the effective ppi, you can define a custom profile that will flag you with a red light:

If you scale an image up, you need to check the effective ppi. If you drop below what your printer recommends, then you need to either to scale the image back down or locate a high-res version of the image.

But it sounds like you knew all this when you asked the question, so are you wishing you had an additional warning on the image? You can put in a feature request here: Adobe InDesign Feedback. The community forums are run by your peers—other users like you—so we can explain features, but we can not change them.

You can optimise your images in Photoshop, work in RGB color mode and ensure the resolution is around 250 to 300PPI at the size you are to print them. If any images have a lower resolution you can you use Image > Image Size in Photoshop to increase the resolution, but as this is done by sampling adjacent pixels don't expect this technique to be very successful on enlarging small images.

Place your images in InDesign. You can check the "Effective PPI" of those images in InDesign's Links panel.