resolution of just 500 is very, very, very small. Right click on the image and then choose properties. This will show you the actual resolution (pixels per inch or PPI). With this information, you can then precisely calculate the largest photo-quality image that can be printed from the file. Simply divide the resolution by 300. Example: A photo with 4,000 x 8,000 pixels can be printed up to 13" x 26".
I think you're using the 500 number as the resolution meaning how many pixels per inch the image could have. For example, my camera shoots at 240 PPI. I can, using Photoshop, increase that number. But that does not explain the actual resolution of the image. You can can have a camera that shoots at 240 PPI with an 18MP, 24MP or even 40MP sensor. The number is basically telling you that based upon how many pixels there are and how close they are, the rate would be 500 pixels per inch. If the image is coming out 4x3, this means that your image has an actual resolution of 1,200 x 900 PPI.