Can you please provide a bit of detail? Specifically, are you making corrections in the text? If so, can you make the corrections in the application that generated the original content? For example, if the content was originally made in (say) MS Word. Can you make the correction there and re-genrate the PDF (that is the best and proper way to do this)? Also, the image will get zero degredation if you use this appraoch.
Unless you do something like "Save a compressed version, you are not likely to damage the image.
And just out of curiosity, what kind of images are these: line art or photograph?