Bitmap to ASCII Converter (abbreviated as BTAC) was an experimental ASCII Art generator, and was written for pretty much no good reason at all. Although the conversion algorithm was very computationally expensive, the results were interesting. BTAC takes a bitmap image (either 8 or 24 bit) and converts it to colored ASCII encoded in HTML.
This application used one of two monospace rasterized fonts (terminal 8pt and terminal 10pt) to find a best-fit symbol for each block of equal dimensions in the bitmap; this allowed for a fair amount of detail to be preserved, especially around edges. BTAC also featured many different adjustable parameters to tweak the conversion process on a per-image basis.
I lost the source code for this application long ago, but that is probably for the best.