Why do I have shadows in my InDesign file when I have images with transparent backgrounds?

I'm think you may have changed your defaults for effects.

Deselect everything and in the Effects panel (Window > Effects). see if there's an fx icon next to one of the listings. If there is, click on the listing and press the Trash at the bottom of the panel.

All new Graphic Frames should work normally now, with no Shadow Effect.

Seeing it where? On screen? In print?

If it's print, does this cover it: https://indesignsecrets.com/eliminating-ydb-yucky-discolored-box-syndrome.php

Hi,

Please indicate what Operating System and InDesign version you are using. Also, a couple of screenshots would help us locate the source of the issue.

There are some areas to check.

1. If this happens to all your images, insert one without transparency. Is there a shadow to that too?
2. Does the same happen when you insert one of your images in a completely new file?
3. Click on the picture frame's edge with your selection tool (black arrow) and check the Fx settings (in the ribbon, top of screen). Click on Drop Shadow to display the settings.
4. Click in the middle of the picture, the bounding box will change colour (often red). Then check the Fx>Drop Shadow settings in case the effect is applied to the picture (and not the frame)
5. In the Object Style panel, check the properties of the default image style, it could be applying the shadow automatically to all images.
6. If that all comes clean, I think it will be part of the image itself