Open the portrait in a photo editing application, such as Photoshop or GIMP.
Duplicate the layer by dragging and dropping it over the "Duplicate" icon at the bottom of the "Layers" palette. Rename this layer "Portrait."
Choose a selection tool and click around the outline of the subject.
Invert the selection to select the background. For example, you can click on the "Select" menu and choose "Inverse" in Photoshop or "Invert" in GIMP.
Press "Delete" on the keyboard to erase the background.
Click the "New Layer" icon in the "Layers" palette to create a colored backdrop layer. When the "Create New Layer" dialog box appears, choose black (for white text) or white (for black text) as the fill color.
Drag this layer beneath the "Portrait" layer.
Select the "Portrait" layer and desaturate it. You can find this option in the "Image" menu under "Adjustments" in Photoshop or in the "Color" menu in GIMP.
Open the "Curves" tool and drag the black point to the right and the white point to the left. Adjust the midtone point until the photo is primarily black, white and middle gray.
Select the "Posterize" filter and set the posterization to Level 3. This reduces the portrait to only three colors: pure black, pure white and middle gray. You can find this effect in the "Image" menu under "Posterize" in Photoshop or under the "Colors" menu in GIMP.
Click on the "Text" tool and create a text box that covers the entire canvas. Fill the box with text.
Create other text boxes and fill them with different sizes and styles of text.
Merge the text layers into a single layer and rename it "Text." In Photoshop, you can do this by Control-clicking on each layer, then choosing "Merge Layers" from the "Layers" menu. In GIMP, click on the "Visibility" icon next to each layer except the text layers to make them invisible, then choose "New From Visible" from the "Layers" menu.
Click on the merged text layer to activate it, then add a layer mask. This option is in the "Layer" menu in Photoshop and in the "Layer" menu under "Mask" in GIMP.
Copy the image from the "Portrait" layer and paste it onto the layer mask on the "Text" layer. For example, in Photoshop, you can click on the "Portrait" layer and press "Control" and "C," then click on the layer mask icon and press "Control" and "V." In GIMP, right-click on the canvas with the "Portrait" layer selected, click "Edit" and select "Copy." Then, click on the layer mask, right-click on the canvas again and select "Paste." Click the "Anchor Layer" icon to apply the copied pixels to the layer mask.
Click on the layer mask to activate it, then invert the selection.
Click on the visibility icon next to each layer except the "Text" layer to make it invisible. You can now view your portrait in black and gray text.
Click on the "Gradient" tool to add a color gradient to your text, if desired.