I have found when flashing some aosp ROMs I get this message. Here's how I fixed it. B4 flashing the ROM move ask your camera pics to external SD card. Then delete the folder where pics are stored on internal SD. I'm not saying this well work for every one bit it worked for me. Try it out and let me know what happens.
Edit: if using twrp you can do this from the file manager in there
Edit: if using twrp you can do this from the file manager in there