Rollpie Image Text Highlighter is a free image highlighter that runs in your browser with no install. Open an image and draw a box around text with “Select + OCR” to recognize it one character at a time, then drag the handles at either end to adjust the highlight one character at a time. Horizontal text is supported.
Pick the marker color from five swatches, or paint freely with the pen and eraser. When you are done, lock it in with “Apply” and export it as an image with “Save”.
Double-click a panel title to switch how the panels are laid out. In the movable layout you drag panels wherever you like and keep several open at once; in the fixed layout a single panel sits in the top right.