It is possible to use Microsoft Paint to remove backgrounds from images like photos, provided you don't mind leaving a solid color behind. By default, erasing any portion of an image leaves behind a white background, however you can change this to any color you want, including a color that is already present in the photo. Because you can't change the size of Paint's Eraser, it's much faster if you cut away as much of the background as possible first. You can then use the Eraser to remove remaining details around the object you want to keep.
Changing Paint's Background Color
Open the image you want to edit in Paint. By default, the Color 2 icon is white, which is the color used to replace anything you cut, erase or delete. Click the "Color 2" icon in the Ribbon if you want to change this color.
Click the eyedropper-shaped "Color Picker" icon if you want to match a color already in the photo to use as the background color. Click on the color in the photo with the Color Dropper. The Color 1 swatch is changed to that color.
Click "Edit Colors." Note that the color you chose from the photo appears as the currently selected color. Click the "Add to Custom Colors" button to add this color to the color palette.
Click the "Color 2" icon and then click the new color that was added to the palette. This changes Color 2 to the new color you picked from the photo.
Removing the Background
Crop out any unneeded details in the photo's background. Click the "Select" icon in the Ribbon, drag the cursor over the main object and then click the "Crop" icon. The more of the background that is cropped out, the less cutting and erasing you will have to do.
Click the down-arrow below the Select icon and click the "Free-Form Selection" option. Using this tool to cut away large sections of the background will save you a lot of time, compared to using the eraser tool.
Drag the cursor around an area of the background to encircle it. Note that when you close the loop you have traced, the line you drew automatically becomes a rectangle. Ignore this rectangle. The line you traced is still there even though you can't see it. Right-click the area you traced and select "Delete."
Zoom in to the photo using the Zoom slider in the bottom right corner of the Paint window. Click the "Eraser" in the ribbon and drag it across the remaining background to delete the pixels. Use short strokes when erasing. If you accidentally erase a part of the object you want to keep, just press "Ctrl-Z" to undo the last stroke.
Zoom out of the photo to make sure you have erased everything. Quite often, you may find colored pixels remaining around the object or in the background in the locations where you used the Free-Form Selection tool. When you're finished, click the "File" menu and select "Save As" to save the image with a new file name.