iphone 3gs numbering of photos limited or infinite?

hi
i have an iphone 3gs 16 gb
and i save the photos to my computer in folders named by the dowload date
not using the itune software,just drag and drop to folder..
then deleting photos randomly
the last time i did that i marked the end point of the roll on the iphone by taking 2 screen shots,that way i can find the spot fast,..copy the photos and then delete all of them from that point.
sure enough,the next time i pluged the iphone to download the photos,i found the marked spot.........but not the photos.
to make a long story short,by sorting the folder "by date taken" all the photos aligned and was found
it seemed that the numbering got screwed up and the photos were placed instead of the deleted ones
so instead of continuing numbering for exemple "IMG_9899" "IMG_9900" the next photo by date recived a number and spot of a deleted one in the begining of the role
today i noticed a new thing
there are duplicate photo numbers one next to the other
is the numbering of photos limited or infinite

help solve this problem pleaase

another problem i have is viewing screen shots of apps in the app store
when i try to slide the screen shots from one to another the whole thing just shake
some times after a few attempts it will slide to the next screen shot

There is likely a limit to the numbers, but that limit is going to be something quite large and has no bearing on this.

My guess is that the each time a photo is saved it determine if there are any photos already, if there aren't any, the number starts at 0 and goes from there. If there are holes in the numbering due to files being selectively deleted, it might re-use this numbers, kinda silly but it might be doing that.

That being the case, the reason you have 2 files named the same is because one of them is a PNG and the other is a JPG, entirely different image formats but with the same name..