Converting .jpg to Text Not Working

[Lyndsweb]

I have Nitro Pro 11. I made screenshots of some pages and saved them individually (auto-format is .jpg), which I then pulled into Nitro and combined them into one .pdf (also tried the below with one of the files, before combining them, with the same result). My primary aim is to convert this to text, which it will not do. I have tried all the following:

1) saving .pdf as standard and flattened, to no effect;

2) Convert to Word - pop-up window says "the selected PDF file contains scanned pages that will appear as bitmap images in the converted PDF file" - problem is I don't want another picture format, I need the text from the 'picture'.

3) OCR - gives the following error message: "OCR was not able to run one or more of the pages within this PDF file. Please view the output pane for more information", which says "OCR did not process page 1 because it has invalid resolution'.

Please help! Is there any way this can be recognised by Nitro and converted to text?!