If you have a photo that you want to remove from your iPhone, of course you can delete it, but finding out how to do it may be a little complicated or trickier.   Photo taken with the iPhone: Open the picture you want to delete and tap the trash icon, then confirms the deletion of the picture.

Photo synced with iTunes: The iPhone maintains a mirror of the files that are on your computer and therefore it is not possible to eliminate pictures from the iPhone. If you remove the photo from the original album on the PC, you see that in the next sync the picture will disappear from the iPhone.