Suppose we have an image with some hidden info behind it. If we open it in a photo manipulation software like Photoshop or Gimp, without editing it and just save it as a new image, does the image still contain the secret info?
If someone is hiding a message within an image using Steganography then the message should be unmolested by simply saving it. Depending on how much the image was modified, and the steganography method used, the message may or may not be readable.
For example if BPCS-Stenography was used to hide the message and you drew a smiley face over the image, then parts of the message will still be readable. If the message was protected by an error correcting code, then the original message maybe entirely intact.
However, if you where to take that same image and convert it to a low quality lossy compression scheme, like jpeg then the BPCS-Steganography message will likely be destroyed.