Can you try changing the Transparency Blend space from Edit Menu..
Does it print like that as well? Sometimes InDesign displays something differently than how it will be printed, especially when it comes to adding effects and transparency settings. The only thing I can think of is that your photo's opacity is turned down or there's a blend mode applied.
Is this for print, web, or EPUB use?
When your Transparency Blend Space is set to CMYK and you add transparency to a page, any grayscales are previewed via your document's CMYK profile showing how it will print on a press with that CMYK profile—the output values are not changing, just the preview. The same thing will happen when you turn on Overprint or Separation Preview.
On pages without transparency InDesign previews grayscales as 2.2 Gamma (the grayscale equivalent of sRGB) when Overprint/Sep preview is off.
You can change your Transparency Blend Space to RGB and stop the preview change, but your grayscales will be converted to 4-color when you export or print to CMYK.
Message was edited by: rob day