Is it worth hiding an AES encrypted text string in a PNG image for better security? I need advice as to whether it is worth the extra "security" and processing of an AES encrypted text string to be hidden in a PNG image as opposed to an AES encrypted text string to be saved in a read-only text file. Both the PNG image and Text file would serve as publicly available AES placeholders that would be decoded via password in a web application. I gather that any hex editor or similar software could access the AES string anyhow, so, would there be any practical benefit security-wise in hiding the AES string in a PNG?
"Hiding" content in an image (or other medium, it's a general technique called steganography) can be done either in a very obvious way (a dedicated data block, called ancillary chunk, which does not form part of the image), or it can be more effectively hidden in the low order bits of the image, thus very subtly degrading the picture. 

Both methods can be discovered by a dedicated analyst, there are even automated tools which can flag images if some telltale statistical anomalies are detected.

This method doesn't add any extra security for the secret message - which is already encrypted anyway. The only thing it provides is a very weak protection of the fact that a secret message existed at all.