With Photoshop Elements or photo editing software you can touch up the area by replicating a good portion of the shirt and using that color and pattern to cover up the stain.
If your work with photos is more serious you may want to start with Photoshop Elements as a less expensive learning platform and then move up to the full Photoshop CS package. With all the power of Photoshop you can perform all of the editing tasks on your images. You can also create complex files for use in print or online. With the companion software ImageReady, you can add fun animation to your Photoshop files for impressive presentations or online ads.
The options for photo editing are varied, but for a reliable, professional program, the best option is Adobe Photoshop either as Elements or the full CS package.
