Your own photographs will be your best source for paintings because they show the subjects you record and reveal your own sense of visual design.  It is also against many rules in Exhibitions to use someone else’s photos.  There are also copyright laws to contend with.

The Digital Age is now so convenient , It allows you to take hundreds of photos quickly for reference.  I would suggest a high memory card for this reason.   Everywhere, someone has a camera to catch a “moment”.  When picking your camera, find one that is convenient to carry, good in low light and high resolution (megapixels).  Because the memory card can store many photos, it is a cheap, convenient process.  Once the image is captured on your memory card, the process is just beginning.  After downloading  the images to your computer, you can manipulate the image in a variety of ways so much so that you can even correct flaws that would otherwise cause you to trash the picture. There are many programs to use to do this.  Many come with your computer or there are websites that offer this also.  Apart from image fixes, there is a whole new realm of creativity where your imagination can run wild.
Invest in a book about taking photos.  Kodak has been doing that and Nikon has a wonderful user manual.  

When taking pictures using natural light indoors, and when using  multiple light, use a tripod.  Use light from a window…It creates great multiple shadows with indoor light and other windows.

Light outdoors:    Best early morning and late afternoon, it creates great shadows….and also in low light, use a tripod.  Night time is also a good source of photography….Use a tripod.  When it is sunny, you need less exposure of light on the picture.  When it is low light, you need more light to come into the camera.  Reflected and indirect light is also fun.   Sunny shade or closed shade…

Use your viewfinder to frame what you want to shoot.  Vary the frame taking the pictures of the same subject and moving the central focus of the picture.  Your camera instructions should guide you through this process.

When you look at the photos you have taken, change the image to black and white.  You can better determine your values.  Also, there are lots of computer programs that you can use to manipulate the photo to enhance what you want to achieve.  Color, Values, Brightness, contrast….to name a few.  You can combine photos to make a better painting.  Also use a projector to draw your subject on to your paper.  There are many to choose from.    

Lots of times when doing this, you may even determine that you could make a wonderful abstract from a simple photo.

Using a camera is taking advantage of today’s technologies and gives you more time to paint and less on the process of preparation.