iColorama has a nice feature that lets you place text in your image along any curve that you define. It is easy to use! Here I show you how to do it, using one of my images as an example.
Open your image in Effects/Txtcurve and tap on Launch, which is in the lower right corner.
By default, Txtcurve opens in Curve mode. Draw the desired curve. NOTE: your text will start where your curve starts. This will affect the orientation of the text. As we will see in the next few steps, in this image, drawing the curve from bottom to top gives the bottom of the text on the right, towards the figure, while drawing the curve from top to bottom has the text facing towards the left, away from the figure (in both cases, the text being to the left of the figure).
Here I've drawn a curve.
Now touch Text, at the top of the screen. Then touch Edit, in the lower right of the screen. A keyboard shows up. Type your phrase on it. Then hit Done. Now you'll see your text along the curve.
Now you'll want to choose a font. Touch Font on the lower right and the available fonts pop up.
Touch the round color icon at the bottom right of the screen, and a color picker comes up. Choose the color of your text. It seems you get only a single color, no stripes or rainbows. Use the sliders to adjust the size of the text and the spacing between the letters. Use the rotate slider to rotate the letters to vertical or some other orientation if you wish. Note that you can't change the direction of the text this way: you can rotate the letters 180 degrees, but then the text will be written backwards!
Touch Shadow to shadow your letters. You can blur the shadow using a slider and set its x and y offset, as well as pick a shadow color.
Now hit close. This will return you to the opening Txtcurve screen. Touch Apply. You're done!