As far as the line that echoes out the img tag, you have several problems:
1. If you are going to wrap a string literal in double quotes, then any literal double quotes within it must be escaped with a back-slash.
2. Looks like you want a style attribute for the width?
3. You need a semi-colon that at the end of the line.
echo "<img src=\"Image.png\" style=\"width:30px;\">";
Alternatively, just use one type of quote to delimit the string literal and the other for literal quotes within the string:
echo "<img src='Image.png' style='width:30px;'>";
Or in this case, since you aren't really using any PHP functionality in that string, just exit out of PHP mode (and also fix your comparison logic!):
<img src="Image.png" style="width:30px;">"
} while ($ImageNumber>=0);
(I strongly recommend the use of the full <?php tag, as short_open_tags may not always be enabled, and it avoids conflict with "<?xml" tags.)