My iPhone says its using more photo memory than it actually is?

My iPhone says it's using 611 mb of memory for my photos but I only have 87 pics and no videos. I hooked my phone to my computer, went into the picture folder and found that the pictures only take up 12.2 mb. How do I fix this?

Added (1). Only 7 of the pictures are actually taken from the camera and they were fairly small. They averaged about 120 kb each. The rest were downloaded from the internet. I did what you said and also doubled checked individually to make sure that the sizes were actually what they said.

Try dragging the images to your desktop and check their sizes. 300KB for an 8MP image is not normal.

If so then you need to check it with the help of your pc and its capacity. If its doesn't fix then you need to format it. Also recheck its memory space of memory and size of picture

Are you sure you didn't sync photos of your computer to your iphone?
you can only view camera roll on your computer…